PC Peripherals for Technicians

PC Peripherals for Technicians
Mar 1998 PC Peripherals for Technicians Chapter 1.1 - Interfaces: Serial Port Systems Manufacturing Training and Employee Development Copyright © 1998 Intel Corp. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 The Serial Port OBJECTIVES: At the end of this section, the student will be able to do the following: Describe UART functions & list the I/O addresses used Discuss the Serial data format & the RS-232C Standard Describe the Registers & Connector signal definitions Discuss the use of loopbacks & Serial BIOS support Describe the Serial Infrared interface. Discuss characteristics and features of modems. Rev 2.0 Sys MFG Training/Employee Development

Serial Port Introduction
PC Peripherals for Technicians Mar 1998 Serial Port Introduction The asynchronous serial port on the PC converts data from parallel form to serial form for communications between computers and external devices. PCs typically support up to 4 serial ports (Com1-Com4). The physical connection consists of an RS-232C standard cable linking the two devices. Other serial port specifications exist, such as RS-422, Bi-Sync, Sync Data Link Control (SDLC), IEEE-488 (GPIB) etc., but the BIOS only supports RS-232C serial ports. The terms “serial port”, “com port”, “RS-232C port”, “serial interface card”, “asynchronous data communications port” are equivalent. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Introduction Serial ports transmit data 1 bit at a time (in a serial fashion), are bi-directional, and are commonly used for communicating with: Telephone modems & fax machines mice & trackballs some printers other PCs (data transfer programs such as Laplink) data acquisition & control Bar code readers, cash registers, scales networks (e.g. AppleTalk) Note: Since all COM ports are the same except for address, this discussion will use COM1 in examples. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Introduction UART REGS: OFFSET 0 Tx BFR(WR); Rx BFR(RD) OFFSET 4 MDM CTL REG (MCR) OFFSET 6 MDM STATUS REG (MSR) 1.84 MHz Oscillator Bi-directional Bus Transceiver Address Decode Logic Chip Select Reset A0 A1 A2 Data D7 - D0 IOR IOW IRQ PC Bus Serial Port RS-232 Interface 9-pin Conn UART Reg P-3 P-4 P-7 P-1 P-9 P-6 P-8 P-2 Tx BFR MCR-0 MCR-1 MSR-7 MSR-6 MSR-5 MSR-4 Rx BFR SOUT DTR RTS DCD RI DSR CTS SIN XIN MR CS2 RD WR INTR OUT2 T x D R x D Addr A9 - A3 -12 1.84 MHz derived from 24MHz/13 on PC87306 Rev 2.0 Sys MFG Training/Employee Development

Universal Async Rcvr Transmitter
PC Peripherals for Technicians Mar 1998 Universal Async Rcvr Transmitter The serial port on a PC is little more than a UART (pronounced “yoo-art”) and RS-232 interface circuitry connected to the PC bus. The PC controls the UART by writing & reading internal registers through a set of I/O ports. The RS-232 interface circuitry converts the UART TTL-level signals into RS-232 signals (+/- 12 Volt). Since about 1990 the UART has been integrated into an LSI chip (ASIC) such as the National Semiconductor PC87308 Super I/O Controller. These chips usually contain 2 UARTS (COM1 & COM2), a parallel port, a floppy disk interface, etc--all in one chip. The RS-232 interface circuitry (line drivers) are external to the Super I/O Controller. Rev 2.0 Sys MFG Training/Employee Development

Universal Async Rcvr Transmitter
PC Peripherals for Technicians Mar 1998 Universal Async Rcvr Transmitter The primary functions of the UART are to: Perform the parallel-serial conversion (and vice versa). Outgoing data is converted from the parallel format used by the PC data bus to the serial format used by the serial port. Incoming serial data is converted to parallel data. Inserting or checking the start, stop & (optional) parity bits. Provide handshaking signals. Request to Send (RTS), Data Set Ready (DSR), etc Simultaneously transmit & receive serial data The UART has separate Transmit & Receive data lines that support full duplex communications. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Enhanced Serial Ports A UART chip was used in terminals & minicomputers for a decade before the first IBM PC came out. The PC COM port is based on chips compatible with the National Semiconductor 8250 which was used in the serial ports of PC or XT computers, This was followed by the 16450, used in the serial ports of (PC/AT) & newer machines, up to about 1996. Functionally the is identical to the 8250, except the read-and-write cycle times are cut in half to keep up with the faster access cycles. Though the can keep up with faster computers (PC/AT), it cannot transfer data any faster because the baud rates are still the same. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Enhanced Serial Ports The next UART was the chip. The is a chip with a FIFO queue - a buffer that holds 16 bytes of incoming or outgoing data. What's received first is moved out first, hence the acronym FIFO (first in, first out) to describe the buffering system. You can't make use of the FIFO features unless the software you are using is aware of the UART chip FIFO buffers aren't accessible unless activated by software. The is otherwise identical to its predecessors and so it can be used as a or 8250 hardware replacement. The was next with a FIFO that holds 32 bytes of incoming/outgoing data. Rev 2.0 Sys MFG Training/Employee Development

Serial Port Names, Addresses, & IRQs
PC Peripherals for Technicians Mar 1998 Serial Port Names, Addresses, & IRQs During POST, the BIOS checks the following I/O Base addresses for UARTS (in this order): 3F8h - 3FFh: BIOS Serial Port 0 - O/S COM1 (DOS, etc) 2F8h - 2FFh: BIOS Serial Port 1 - O/S COM2 3E8h - 3EFh: BIOS Serial Port 2 - O/S COM3 2E8h - 2EFh: BIOS Serial Port 3 - O/S COM4 Each serial port is accessed as a set of eight consecutive I/O registers offset from the Base Address To detect an active port, some versions of BIOS read the Interrupt ID Register at Base+2 (e.g. 3FA). If bits 7-3 are 0, the POST considers this an active port. Note: Some BIOS versions don’t check for COM3/4. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Names, Addresses, & IRQs The BIOS stores the base addresses (2 bytes) of detected serial ports in consecutive locations in a table starting at main memory address 0x40:0. This is the BIOS Data Area (400h-500h) The BIOS can manage up to four different UARTs, because the table has four entries. The first entry in the BIOS table at 0x400 (40:0) is COM1 The COM1 serial port base address is most often 0x3F8 0000:0400 F8 03 (03F8h stored in little endian format) the 2nd (40:2) COM2; the 3rd (40:4) COM3 and the 4th (40:6) COM4 (if there are that many). Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Names, Addresses, & IRQs There are only two IRQ lines assigned for use by COM ports: IRQ 3 and IRQ 4 In theory, this means that you can only have a maximum of two serial ports. However, you can have more (i.e. COM3 and COM4) by sharing the interrupts. By convention, COM 1 & COM 3 share the IRQ4 line and COM 2 & COM 4 share the IRQ3 line. Note: You cannot use these ports simultaneously (i.e. COM 1 and COM 3) when sharing interrupts unless they are being controlled by the same application Some serial cards allow you to select non-standard IRQ's: Typically any of IRQ’s 2,3,4,5,7 or 9-13 might be used . Rev 2.0 Sys MFG Training/Employee Development

Asynchronous Serial Communications
PC Peripherals for Technicians Mar 1998 Asynchronous Serial Communications The information contained in the serial bit stream is represented by codes that are each transmitted for a fixed time period known as the Baud Period. One bit is transmitted during each baud period. The transmit & received clocks must be synchronized and be the same baud rate. This is asynchronous - the receiver resynchronizes itself to the transmitter using the start bit of each frame. Baud Rate is the number of Bits Per Second (1/[baud period]) transmitted or received by the serial port . The Serial Port Baud Rate is not the same as the number of data bits to or from CPU due to the additional Start, Stop, & Parity bits inserted by the UART. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Asynchronous Serial Communications The serial frame consists of a combination of the start, data, parity, and stop bits. The frame size depends on UART control options selected by software. The data portion can be 5-8 bits. (Reset default = 5 bits ) The parity bit can be optionally included One or two stop bits can be selected. The serial framing protocol is usually described by a sequence of numbers and letters. e. g. 8n1 means 8 bits of data, no parity bit, 1 stop bit, and 1 start bit (always the same, thus omitted). e.g. 7e1 would indicate 7 bits of data, even parity, 1 stop bit. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Asynchronous Serial Communications The start bit indicates the beginning of a new single character & synchronizes the transmitter and receiver. It is always a logical '0' as output from the UART. Data is transmitted LSB to MSB: The least significant bit (LSB, Bit 0) is transmitted first with 4 to 7 bits of data following, resulting in 5 to 8 bits of data per frame. The PC is capable of serial transmission at up to 115,200 bps. Standard rates are 300, 1200, 2400, 4800, 9600, 14400, 19200, 38400, and bps . Baud rates are derived by dividing the 1.84 MHz input by the divisor specified in the Divisor Latch registers. The 1.84 MHz derived from 24MHz/13 on the PC87306. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Asynchronous Serial Communications A parity bit can be added to the data bits to allow error detection. Two types of parity are commonly used: odd and even. Odd parity means that the number of 'ones' or ‘mark’ bits in the data byte (including an optional parity bit, but not the framing bits) is always odd, so the parity bit is set accordingly. The stop bit separates two consecutive bytes by putting the line into the quiescent state (the stop bit is a logical '1') for a minimum time in order for the next start bit (a logical '0') to be clearly visible. Rev 2.0 Sys MFG Training/Employee Development

The RS-232C Interface Standard
PC Peripherals for Technicians Mar 1998 The RS-232C Interface Standard RS-232 is officially known as Electronics Industries Association (EIA) Standard RS232C for low speed serial data communication.. RS-232 is intended for relatively short distances (50 feet or less), and relatively low speed (19,200 bits per second or less) serial communications. The RS-232C interface standard defines various connection parameters, including connector type, I/O signal levels, line names, and pin numbers. The DB-25S and DB-25P (25-pin) connectors (sometimes called "EIA connectors") are recommended, but are not mandatory. PC compatible computers commonly use a 9-pin D-sub (DB-9S) male connector. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The RS-232C Interface Standard Much of the RS-232 standard is concerned with support of Modems. There are two main classes of RS-232 devices: DTE (Data Terminal Equipment) Computers (PCs) and terminals are called (DTE). DCE (Data Communication Equipment) Modems are Data Communications Equipment (DCE). Typically a serial port on a PC is considered DTE and a modem DCE. IBM saw the original PC as a Terminal device (DTE), meant to be connected to a mainframe (DCE) As a result, all PCs have DTE serial interfaces. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The RS-232C Interface Standard The RS-232 standard defines a set of wires that run between the DTE and DCE devices. Signal names are from the viewpoint of the DTE (PC). The ground is the reference point against which all the signals are measured. The wire carrying data from the computer to the modem is called the Transmit wire (Transmit Data, TD or TxD), i.e. Transmit Data is data being sent by the DTE (PC), but received by the DCE (modem). The wire carrying data in the opposite direction is called the Receive wire (Receive Data, RD or RxD) Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The RS-232C Interface Standard Note: PC systems commonly use +/- 12 volts & the voltages are with respect to the Signal Ground line. RS-232 data looks upside down compared to normal logical systems and the signals are not TTL levels: Voltage Data Signal Control +3 to SPACE On -3 to MARK Off This dates back to the teletype protocol which used a current loop to continuously monitor the state of the line. Current flow was regarded as a “1” & was “MARK”-ing time A DATA signal then left a “SPACE” in the graph of the current flow designating a zero. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The RS-232C Interface Standard Using an O’scope to view the Serial Data 5B hex Note that RS-232 looks upside down compared to normal logical systems: Start Bit (Logical 0) = RS V Using 2400 baud rate: 1 / 2400 = 417 microseconds Bit stream in binary is (LSB first, MSB last) 417 uS 4.17 ms 1 + 12v RS-232 - 12v START STOP BIT BT BT BT BT BT BT BT BT BIT LSB MSB 0V TTL +5V Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Serial Port Pinout Serial Port DB9-Male DB25-Male 9-pin 25-pin assignment 1 8 DCD (Data Carrier Detect) 2 3 RD (Receive Data) 3 2 TxD (Transmit Data) 4 20 DTR (Data Terminal Ready) 5 7 GND (Signal Ground) 6 6 DSR (Data Set Ready) 7 4 RTS (Request To Send) 8 5 CTS (Clear To Send) 9 22 RI (Ring Indicator) Looking at PC Serial Port DB-9S Connector (Male) DCD RxD TxD DTR GND DSR RTS CTS RI The input & output signals are made available through a 9-pin or 25-pin, D-type connector. This male connector protrudes through the rear panel of the system, where a cable may be attached. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Serial Port Registers Debug techs may have occasion to use the following registers, usually with a loopback connector attached. When debugging Serial Port problems, the majority of the system board should be functional and using BIOS interrupts in “procs” with a debug tool such as the In Target Probe is fast and practical. A COM port occupies 8 consecutive I/O addresses COM1 starts at 03F8 and ends at 03FF COM2 starts at 02F8 and ends at 02FF. Each of these one byte addresses performs a specific function. Note: A detailed description of UART programming is outside the scope of this course. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Serial Port Registers Port 0x3F8 is used to transfer data (TxD, RD) Anything written to 03F8 will be sent to the output, if the appropriate handshake signals are asserted. Reading from 03F8 will obtain the next byte of data. Writing to the Modem Control Reg (Port 3FC) provides control of output signals sent to the connector. Use to Set/Clear DTR (MCR bit 0) & RTS (MCR bit 1) Reading the Modem Status Register (Port 0x3FE) reports the status of input signals on the connector. Read state of the DCD, RI, DSR, & CTS (MSR bits 7-4). There are also addresses to set the speed, parity, stop bits, and character size. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Serial Port Registers COM1 Base Addr Register 3F8 Base+0 Receive buffer (read) (if LCR bit 7=0) 3F8 Base+0 Transmit buffer (write) (if LCR bit 7=0) 3F8 Base+0 Divisor latch low byte (if LCR bit 7=1) 3F9 Base+1 Interrupt Enable (IER) (if LCR bit 7=0) 3F9 Base+1 Divisor latch high byte (if LCR bit 7=1) 3FA Base+2 Interrupt Flag Register (IFR) 3FB Base+3 Line Control Register (LCR) 3FC Base+4 Modem Control Register (MCR) 3FD Base+5 Line Status Register (LSR) 3FE Base+6 Modem Status Register (MSR) 3FF Base+7 Scratch pad (Not in original UART) Set LCR (3FB) Bit 7=1 to program the baud rate (divides the 1.84 MHz Oscillator by the specified divisor in 3F8 &3F9). Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 Serial Port Registers UART REGS: OFFSET 0 (3F8) Tx BFR (WRITE) Rx BFR (READ) OFFSET 4 (3FC) MDM CTL REG (MCR) OFFSET 6 (3FE) MDM STATUS REG (MSR) UART Reg Tx BFR MCR-0 MCR-1 MSR-7 MSR-6 MSR-5 MSR-4 Rx BFR Serial Port RS-232 Interface SOUT DTR RTS DCD RI DSR CTS SIN XIN MR A0 A1 A2 CS2 D7 - D0 RD WR INTR OUT2 T x D R x D -12 Rev 2.0 Sys MFG Training/Employee Development

Hardware & Software Handshaking
PC Peripherals for Technicians Mar 1998 Hardware & Software Handshaking Handshaking is a method of exchanging signals for data flow control between computers. Hardware: RTS & CTS (Request To Send & Clear To Send) have been specially designed for data flow control. Used with UARTS & modems which transfer binary data. Software: An often used software protocol is called XON/XOFF (Transmission On / Transmission Off). Uses two bytes in the ASCII character set: XON (11h, Ctrl-Q, DC1); XOFF (13h, Ctrl-S, DC3). One of the sides sends an XOFF to interrupt the data flow. Used for Text transfers only - won’t contain 11h or 13h. Often used with terminals, printers, & plotters. e.g. - “CTRL-S” stops scrolling of text on the terminal. Rev 2.0 Sys MFG Training/Employee Development

DESCRIPTION OF COMMON SIGNALS
PC Peripherals for Technicians Mar 1998 DESCRIPTION OF COMMON SIGNALS A typical Serial Transmit control sequence example: 1. The PC (DTE) asserts DTR (Data Terminal Ready) to indicate that it is active and ready for transmission. 2. The Modem (DCE) responds by asserting the DSR line (Data Set Ready), indicating that it is also ready for communications. 3. The PC (DTE) asserts the RTS line (Request To Send) to indicate that it is ready to start transmitting. 4. The Modem (DCE) responds by asserting the Clear To Send line, indicating that it is ready to receive data. 5. Data is now transmitted on the TD and RD lines. Cannot transmit until DTR, DSR, RTS, & CTS =1 6. The PC drops Data Terminal Ready to disconnect. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 DESCRIPTION OF COMMON SIGNALS See the ‘Appendix A’ for a more complete description of the signals. TxD (Transmit Data): Output - Pin 3 Data is sent from the DTE (PC) to the DCE (modem) Cannot transmit until DTR, DSR, RTS, & CTS =1 RD, RxD, Sin (Receive Data): Input - Pin 2 Serial data is sent from the DCE to the DTE (PC). GND, SG (Signal Ground): Pin 5 This is the ground to which all other voltages are relative. The following control lines each have two states. High or asserted (+12v) state indicates the control line is active -- the CONTROL signal is ON. Low (de-asserted) state indicates the line is inactive. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 DESCRIPTION OF COMMON SIGNALS DTR (Data Terminal Ready): Output - Pin 4 This signal informs the DCE (modem, fax, etc) that the DTE (PC) is powered up and ready to go. Set to +12v (Control Signal ON) by MCR bit 0 = 1 e.g. write 01h ( y) to 3FCh [ITP uses ‘y’ for binary] Note: This sets DTR# = 0 (from the UART) which is inverted to +12v by the RS-232 interface circuitry (line driver). DSR (Data Set Ready): Input - Pin 6 This signal informs the DTE (PC) that the DCE (modem, fax, etc) is powered up and ready to go. +12v sets MSR bit 5 = 1 e.g. read 20h ( y) from 3FEh [Modem Status Reg] NOTE: Loopbacks typically tie DTR to DSR. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 DESCRIPTION OF COMMON SIGNALS RTS (Request To Send): Output - Pin 7 Indicates that the DTE (PC) wishes to send data to the DCE (modem, fax, etc) Set to +12v by MCR bit 1 = 1 e.g. write 2h ( y) to 3FCh [Modem Control Reg] CTS (Clear To Send): Input - Pin 8 Indicates that the DCE (modem, fax, etc) is ready to accept data from the DTE (PC). +12v sets MSR bit 4 = 1 e.g. read 10h ( y) from 3FEh [Modem Status Reg] NOTE: Loopbacks typically tie RTS to CTS. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 DESCRIPTION OF COMMON SIGNALS RI (Ring Indicator): Input - Pin 9 The DCE (modem, fax, etc) indicates to the DTE (PC) that the phone line connected to the attached device (modem) is ringing. +12v sets MSR bit 6 = 1 e.g. read 40h ( y) from 3FEh [Modem Status Reg] DCD (Data Carrier Detect): Input - Pin 1 This is the signal the DCE (modem, fax, etc) uses to inform the DTE (PC) that it has detected a carrier signal. +12v sets MSR bit 7 = 1 e.g. read 80h ( y) from 3FEh [Modem Status Reg] Rev 2.0 Sys MFG Training/Employee Development

Serial Port Loopbacks & Testing
PC Peripherals for Technicians Mar 1998 Serial Port Loopbacks & Testing A Loopback Connector has some of the output pins wire connected to some of the input pins. When placed on the board's serial port connector, data sent out is received back by the same port. DCD RxD TxD DTR GND DSR RTS CTS RI Looking at DB-9S Connector (Male) A common serial loopback is a female 9-pin D-sub connector with the following pins wired together. RTS (pin 7) - (pin 8) CTS - (pin 1) DCD Registers : MCR-bit 1 to MSR-bit 4 to MSR-bit 7 DTR (pin 4) - (pin 6) DSR - (pin 9) RI Registers : MCR-bit 2 to MSR-bit 5 to MSR-bit 9 SOUT [TxD] (pin 3) - (pin 2) SIN[RD] Registers: Xmit Buffer (write) & Rcv Buffer (read) Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Loopbacks & Testing Testview provides comprehensive diagnostics designed to test the functionality of the serial ports. One test of the serial port checks the 8-bit data bus to the UART and it’s ability to transmit and receive data with and without the loopback connector attached. This is accomplished by writing data patterns to the serial controller (at port 0x3F8) & reading the data back. The Line Control Register is configured for 8 data bits. This can also be set by writing 03h to Port 3FB with the ITP. Then the UART is tested by transmitting bytes such as 0xf0, 0xcc, 0xaa, and 0x55. If the four bytes are successfully received as they are looped back, the test passes. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port Loopbacks & Testing The UART can be tested without the external loopback by setting Bit 4 of the Modem Control Register to place the controller into Internal loopback mode. Writing 10h ( y) to Port 3FCh sets bit 4 of MCR. The xmit & rcv data buffers are internally looped back & some control outputs are internally connected to inputs. RTS# - CTS#; DTR# - DSR#; OUT1# - RI#; OUT2# - DCD# i.e. MSR bit 4 (CTS) shows the state of RTS (MCR bit 1). If the UART passes the internal loopback test, but fails with the external loopback attached: Suspect the connector or lines to/from the connector or the RS-232 interface circuitry (usually implemented externally) Make sure that the external loopback connector is properly seated and is wired correctly. Rev 2.0 Sys MFG Training/Employee Development

Serial Port BIOS Support
PC Peripherals for Technicians Mar 1998 Serial Port BIOS Support Serial port support by the ROM BIOS uses INT 14h and is very limited, but can be useful for looping with ITP debug procs. The BIOS functions historically do not use the serial port interrupt feature, but use software timing loops instead. Programs that do not use interrupts are speed restrained because the UART must be polled frequently to prevent character loss. NOTE: Many commercial communications programs access the UART directly and use interrupts to maximize performance. An interrupt is generated whenever a character is received by the port, or to request another byte when a previous block of data has been sent to the modem. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port BIOS Support Call INT 14h with AH=0 to initialize the port DX = port number (00h-03h) - e.g. DX=00 for COM1 AL = port parameters (see below) Bit(s) Description 7-5 data rate (e.g. 300, 2400, 9600 bps etc) 4-3 parity (00 or 10 = none, 01 = odd, 11 = even) 2 stop bits (set = 2, clear = 1) 1-0 data bits (00 = 5, 01 = 6, 10 = 7, 11 = 8) Return : AH = line status (see AH=03h in Appendix B) Calling INT 14h with AH =0 and AL= a3h ( y), selects 2400 baud, no parity, 1 stop, & 8 data bits. Note: Writing 03h to Port 3FB (Line Control Reg ) with an ITP will also select 8 data bits, 1 stop bit, & no parity. A hardware reset sets the default number of data bits to 5. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Serial Port BIOS Support Call INT 14h with AH=1 to send a byte to a port. AH = 01h; AL = character to write DX = port number (00h-03h) Return: AH bit 7 clear if successful AH bit 7 set on error AH bits 6-0 = port status (see AH=03h in Appendix B) Call INT 14h with AH=2 to read a byte from a port. AH = 02h; DX = port number (00h-03h) Return: AH bit 7 clear if successful AH = line status (see AH=03h) AL = received character if AH bit 7 clear See App B for information on AH=3 Rev 2.0 Sys MFG Training/Employee Development

The Serial Infrared Interface
PC Peripherals for Technicians Mar 1998 The Serial Infrared Interface Infrared (IR) connectivity allows for the wireless exchange of data between computer devices such as: Desktop/laptop/notebook PCs, printers, fax machines, network nodes, data modems, telephones, automated tellers, PDAs, electronic organizers, etc. The Infrared Data Association (IrDA) is a group of component, computer system, & peripheral vendors. The IrDA standard for wireless data communications uses high-speed, infra-red communications (the same basic technology used in TV remote controls) IrDA provides for data to be transmitted/received at a speed of 9.6Kbps to 4.0Mbps, at distances of up to three meters, and with a reception angle of 30 degrees. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The Serial Infrared Interface The IR transmit interface translates the data from the UART into pulses which are output through an LED. The LED translates "data" current into "data" photons. The IR receive interface uses a lensed photo diode detector that receives the "data" photons from the transmitter and translates it back into "data" current. Connected to Header on motherboard Implemented in PC87308 Tx Rx RS-232 IR Interface Infrared LEDs Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The Serial Infrared Interface The physical layer is based on the common serial port, with a few adaptations to reduce the "on" period power requirements (reduces drain on batteries in laptops). The IrDA interface is limited to half-duplex operation due to interference from the reflected transmit signal. The physical interface consists of: Encoder / Decoder (IR transmit / IR receive) interfaces to the UART, commonly on COM2 which can be configured as a normal (modem) port or an IR port. Often integrated into “super I/O” chips (e.g. National 87308). The IR Transducer consists of the output driver and IR emitter for transmitting, and the receiver/detector. Often connected to system board front panel I/O header. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 The Serial Infrared Interface Testing the infrared signals on the motherboard (normally COM2), is often accomplished using a “dongle” on the UUT serial port (normally COM1). A “dongle” such as the ESI-9680A JETEYE RS232-to-IRDA device manufactured by Extended Systems The test sets the IR serial port (COM2) and the dongle serial port (COM1) to Kbaud & "8N1". The IR serial port COM2 transmits a sequence of bytes. If the dongle serial port (COM1) receives this sequence from the IR serial port, the dongle serial port (COM1) then transmits another sequence of bytes. If the IR serial port (COM2) receives this sequence from dongle serial port (COM1), the test passes. Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Introduction
PC Peripherals for Technicians Mar 1998 Modem Overview - Introduction A MOdulator/DEModulator converts data bits to sound, so data can be transmitted through an ordinary phone system. Modems also provide data compression, error recovery, and some telephone services (e.g. dialing). Personal Computer Modem Compression Decompression 19,200 bps 9600 bps Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Modem Overview - Introduction A modem converts digital signals generated by the computer into analog signals which can be transmitted over a telephone line--and transforms incoming analog signals into their digital equivalents. Receive Data Transmit Data To analog Telephone Lines Modem (DCE) RS Serial Data 0 = +12Vdc 1 = -12Vdc Serial Port (DTE) Microprocessor Parallel Data TTL DATA 0 = 0Vdc 1 = +5Vdc System Board UART & XCVR Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Modem Overview - Introduction When the system is transmitting data to another system: The CPU writes a data byte (8 bits) to the serial port. The serial port serializes the data and converts the TTL 1’s and 0’s to the voltage level understood by the modem (RS-232). The modem converts the RS-232 1’s and 0’s to audio and sends it over the telephone line to the other computer system. The UART interrupts the CPU to request another byte. Continued on next page. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 Modem Overview - Introduction When the system is receiving data from another system: The modem receives the audio data over the telephone line, demodulates it, and sends the serial bit stream to the UART. The serial port converts the RS-232 1’s and 0’s to the TTL voltage levels understood by the system. The UART interrupts the CPU when it has a byte assembled The CPU jumps to the serial port’s Interrupt Service Routine. The ISR inputs the data byte and stores it in memory. Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Standards
PC Peripherals for Technicians Mar 1998 Modem Overview - Standards Consultative Committee on International Telephone and Telegraph (CCITT) - See App C for more information Renamed ITU (International Telecommunications Union) Also known as the "V dot" standards (e.g V.32). When a standard is upgraded, it is labeled "bis", which is French for "2nd" (e.g V.42bis); "ter" would be the 3rd version Most modems use a standardized set of instructions called the "Hayes (a modem mfg) command set" Modems have both a command mode and a data mode. The Hayes modem instructions begin with a two character sequence called the "attention character" - the letters “AT”. Other characters specifying the command follow the “AT” e.g. ATDT Dial using Tones. e.g. ATH0 - Hangs up the phone. Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Compression
PC Peripherals for Technicians Mar 1998 Modem Overview - Compression Data compression standards use a variety of statistical techniques to pack more data into fewer bits. Data compression algorithms exploit redundancies in data files, especially text files and certain graphics formats, by substituting a few characters for many. For example, a repeated string of characters like "AAAAAAAA" can be compressed to something like "A|8" meaning "character 'A' repeated eight times." Common letter combinations, such as "the", can be compressed and represented by single characters. There are two major standards for data compression protocols, MNP5 and CCITT V.42bis MNP-5 - approximately 2-to-1 data compression. CCITT V.42bis - compresses data to a max 4-to-1 ratio. Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Modulation Methods
PC Peripherals for Technicians Mar 1998 Modem Overview - Modulation Methods Low speed modems use FSK (Frequency Shift Keying) A constant frequency sine wave (called the 'carrier') is shifted to a slightly higher or slightly lower frequency to represent a logic 0 or logic 1, respectively. Bell-103 Modem originate-mode signal frequencies (300 Baud) Telephone System Bandwidth 300 3000 1070 Space 2025 1270 Mark 2225 Frequency (Hz) Transmit Receive Serial bit stream Frequency- shift keying Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Modulation Methods
PC Peripherals for Technicians Mar 1998 Modem Overview - Modulation Methods A telephone channel typically has a useful bandwidth of about 2700 Hz (from 300 to 3000 Hz) Using both an originate carrier and an answer carrier to simultaneously transmit and receive data, a full duplex modem can send & receive information at the same time. Rates above 1200 baud use more complex PSK or QAM modulation methods to transmit more information within the standard telephone bandwidth limits. PSK (Phase Shift Keying) QAM (Quadrature Amplitude Modulation) Note: “baud rate” (carrier shifting rate) and the “data rate” (bits per second) are not the same when using PSK/QAM. Note: See chart in Appendix C for more information on Modem Standards. Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Null Modem Interface
PC Peripherals for Technicians Mar 1998 Modem Overview - Null Modem Interface DTE DCE Transmitted Data Received Data 2 3 PC to modem RS-232 interface. PC Modem Transmitted Data Received Data PC #1 2 3 Computer to computer RS-232 interface mismatch. DTE PC #2 Transmitted Data Received Data 2 3 Null Modem DTE PC #1 PC #2 Null modem interface Rev 2.0 Sys MFG Training/Employee Development

Modem Overview - Null Modem Interface
PC Peripherals for Technicians Mar 1998 Modem Overview - Null Modem Interface When you connect one personal computer to another without using modems (over a cable connected via the serial-port), you need a "null modem" connection. A null modem cable is different from a normal modem cable in that the receiving and transmitting pins are reversed. Function Pin# Pin# Function Signal Ground Signal Ground Transmit Data (out) Receive Data (in) Receive Data (in) Transmit Data (out) Request to Send (out) Data Carrier Detect (in) Clear to Send (in) 8 Data Carrier Detect (in) Request to Send (out) 8 Clear to Send (in) Data Terminal Ready (out) Data Set Ready (in) Data Set Ready (in) Data Terminal Ready (out) Standard Null-Modem Cable - PC/AT to PC/AT (DB-9S to DB-9S) Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 REVIEW & SUMMARY UART REGS: OFFSET 0 Tx BFR(WR); Rx BFR(RD) OFFSET 4 MDM CTL REG (MCR) OFFSET 6 MDM STATUS REG (MSR) 1.84 MHz Oscillator Bi-directional Bus Transceiver Address Decode Logic Chip Select Reset A0 A1 A2 Data D7 - D0 IOR IOW IRQ PC Bus Serial Port RS-232 Interface 9-pin Conn UART Reg P-3 P-4 P-7 P-1 P-9 P-6 P-8 P-2 Tx BFR MCR-0 MCR-1 MSR-7 MSR-6 MSR-5 MSR-4 Rx BFR SOUT DTR RTS DCD RI DSR CTS SIN XIN MR CS2 RD WR INTR OUT2 T x D R x D Addr A9 - A3 -12 1.84 MHz derived from 24MHz/13 on PC87306 Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 REVIEW & SUMMARY WE HAVE DISCUSSED THE FOLLOWING: The primary functions of the UART. Perform the parallel-serial conversion (and vice versa). Inserting or checking the start, stop & parity bits. Provide handshaking signals. Simultaneously transmit & receive serial data. The addresses used by the serial port. 3F8h - 3FFh: BIOS Serial Port 0 - O/S COM1 (DOS) 2F8h- COM2; 3E8h- COM3; 2E8h - COM4 Asynchronous Serial Communications data format. Serial frame consists of start, data, parity, & stop bits. 8n1 means 8 bits of data, no parity bit, 1 stop bit. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 REVIEW & SUMMARY The RS-232C interface standard. 2 classes of devices: PCs are DTE; Modems are DCE. Signal names are from the viewpoint of the DTE (PC). Looks upside down: Start Bit (Logical 0) = RS V Serial Port registers & input/output signal definitions. Writing to the Modem Control Reg (Port 3FC) provides control of output signals sent to the connector. Reading the Modem Status Register (Port 3FE) reports the status of input signals on the connector. The use of loopbacks for testing serial ports. Some output pins wire connected to some input pins. Can be tested without the external loopback by setting Bit 4 of the MCR to place into Internal loopback mode. Rev 2.0 Sys MFG Training/Employee Development

Mar 1998 REVIEW & SUMMARY Serial port BIOS support. ROM BIOS uses INT 14h and is very limited. Call INT 14h with AH=0 to initialize the port. The Serial Infrared interface. The physical layer is based on the common serial port. IR transmit / IR receive commonly on COM2. The IR Transducer connected to front panel I/O header. Characteristics and features of modems. A MOdulator/DEModulator converts data bits to sound. Modems use FSK, PSK & QAM modulation methods. A "null modem" cable connects one PC to another without using modems. End of Chapter 1-1 Rev 2.0 Sys MFG Training/Employee Development

APPENDIX A: RS-232 SIGNAL DESCRIPTION
PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION A typical Serial Transmit control sequence example: 1. The PC (DTE) asserts DTR (Data Terminal Ready) to indicate that it is active and ready for transmission. 2. The Modem (DCE) responds by asserting the DSR line (Data Set Ready), indicating that it is also ready for communications. 3. The PC (DTE) asserts the RTS line (Request To Send) to indicate that it is ready to start transmitting. 4. The Modem (DCE) responds by asserting the Clear To Send line, indicating that it is ready to receive data. 5. Data is now transmitted on the TD and RD lines. Cannot transmit until DTR, DSR, RTS, & CTS =1 6. The PC drops Data Terminal Ready to disconnect. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION TxD (Transmit Data): Output - Pin 3 Serial data is sent from the DTE (PC) to the DCE (modem, fax, etc) RD, RxD, Sin (Receive Data): Input - Pin 2 Serial data is sent from the DCE to the DTE (PC). GND, SG (Signal Ground): Pin 5 This is the ground to which all other voltages are relative. The following control lines each have two states. The high or asserted state indicates that the control line is active. The low or de-asserted state indicates that the control line is inactive. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION DTR (Data Terminal Ready): Output - Pin 4 Set to +12v (Control Signal ON) by MCR bit 0 = 1 e.g. write 01h ( y) to 3FCh [ITP uses ‘y’ for binary] Note: This sets DTR# = 0 (from the UART) which is inverted to +12v by the RS-232 interface circuitry (line driver). This signal informs the DCE (modem, fax, etc) that the DTE (PC) is powered up and ready to go. The DTE (PC) indicates to the DCE that it is ready to respond to signals and data from the DCE (modem) . Can be set to the ON state by the DTE (PC) when a comm program is loaded and the PC is ready to communicate. Note that a typical DCE (modem, etc) must have an incoming DTR before it will function normally. NOTE: Loopbacks typically tie DTR to DSR. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION DSR (Data Set Ready): Input - Pin 6 +12v sets MSR bit 5 = 1 (e.g. read 20h from 3FEh) This signal informs the DTE (PC) that the DCE (modem, fax, etc) is is powered up and ready to go. DCE indicates that it is available to transmit data. Sometimes called “modem ready”. It is normally set to the ON state by the DCE (modem, fax, etc) upon power-up and left there. Note that a typical DTE (PC) must have an incoming DSR in order to function normally. NOTE: Loopbacks typically tie DTR to DSR. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION RTS (Request To Send): Output - Pin 7 Set to +12v by MCR bit 1 = 1 (e.g. write 2 to 3FCh) Indicates that the DTE (PC) wishes to send data to the DCE (modem, fax, etc) The DTE requests permission to send information on the TxD line and awaits an ON condition on CTS (Clear to Send) from the DCE (modem, fax, etc), The DTE must leave this line high throughout the entire transmission sequence. Many modems will hang up the phone line when RTS goes low. NOTE: Loopbacks typically tie RTS to CTS. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION CTS (Clear To Send): Input - Pin 8 +12v sets MSR bit 4 = 1 (e.g. read 10h from 3FEh) Indicates that the DCE (modem, fax, etc) is ready to accept data from the DTE (PC). The DCE (modem) responds to the RTS signal on the Clear to Send control line. The DTE (PC) cannot transmit until CTS is set high. Note that a typical DTE (PC) must have an incoming CTS before it can transmit. NOTE: Loopbacks typically tie RTS to CTS. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION DCD (Data Carrier Detect): Input - Pin 1 +12v sets MSR bit 7 = 1 (e.g. read 80h from 3FEh) This is the signal the DCE (modem, fax, etc) uses to inform the DTE (PC) that it that it has detected a carrier signal. The attached device (Modem) has established a link with another modem. Note that some DTEs (PCs) must have an incoming DCD before they will operate. Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians Mar 1998 APPENDIX A: RS-232 SIGNAL DESCRIPTION RI (Ring Indicator): Input - Pin 9 +12v sets MSR bit 6 = 1 (e.g. read 40h from 3FEh) The DCE (modem, fax, etc) indicates to the DTE (PC) that the phone line connected to the attached device (modem) is ringing. This line is typically used to tell a modem to answer the line. Often used by communications software to automatically answer an incoming call. Rev 2.0 Sys MFG Training/Employee Development

APPENDIX B - Serial Port BIOS Support
PC Peripherals for Technicians Mar 1998 APPENDIX B - Serial Port BIOS Support Call INT 14h with AH=3 to read status from a port. AH = 03h; DX = port number (00h-03h) Return: AH = line status; AL = MODEM status Bit fields for line status: 7-timeout; 6-transmit shift register empty; 5-transmit holding register empty; 4-break detected; 3-framing error; 2-parity error; 1-overrun error; 0-receive data ready Bit fields for modem status: 7-carrier detect; 6-ring indicator; 5-data set ready; 4-clear to send; 3-delta carrier detect; 2-trailing edge of ring indicator; 1-delta data set ready; 0-delta clear to send Call INT 14h with AH=4 for Extended Initialization or AH=5 for Extended Comm Port Control on PS/2 & many later systems. Includes initialization at baud rates at 19,200 & 115,200. Rev 2.0 Sys MFG Training/Employee Development

APPENDIX C: MODEM STANDARDS
PC Peripherals for Technicians Mar 1998 APPENDIX C: MODEM STANDARDS Standard Description (Note: ITU formerly CCITT) Bell 103J AT&T standard for full duplex modem operation at 300 bps using frequency-shift keying. Bell 212A AT&T standard for full duplex modem operation at 1200 bps using differential PSK to send two bits baud period at 600 baud. V.22bis ITU standard for full-duplex modem operation at 2400 bps using quadrature amplitude modulation (QAM) to send four bits per baud period. V.32 ITU standard for full-duplex synchronous modem operation at bps to send 4 data bits per baud period at 2400 baud. V.32bis ITU standard for full-duplex synchronous modem operation at 14,400 bps to send 6 data bits per baud period at 2400 baud. V.34 ITU standard for full-duplex synchronous modem operation at 28,800 bps to send a variable number of bits per baud period. V.42 ITU standard for error control of modem data. Data is transmitted in blocks with a cyclic redundancy checksum appended to the end of each block.. V42bis ITU standard for on-the-fly modem data compression. Compression ratios of about 3:1 are typically achieved. Rev 2.0 Sys MFG Training/Employee Development

APPENDIX C: MODEM STANDARDS
PC Peripherals for Technicians Mar 1998 APPENDIX C: MODEM STANDARDS Modem Type (BPS) Modulation Asynch/Synch Duplex Mode Bell FSK Asynch Full Bell 212A 1200 PSK Asynch Full CCITT V PSK Asynch Full WE 201A 2400 PSK Synch Half WE 201B 2400 PSK Synch Full WE 201C 2400 PSK Synch Full CCITT V PSK Synch Full CCITT V.26 bis 2400 PSK Synch Half CCITT V.26 ter 2400 PSK Synch Full CCITT V.22 bis 2400 QAM A or S Full CCITT V PSK Synch Full CCITT V.27 bis 4800 PSK Synch Half CCITT V.27 ter 4800 PSK Synch Full Bell 208A 4800 QAM Synch H or F Bell 208B 4800 QAM Synch Half Bell 209A 9600 QAM Synch Full CCITT V QAM Synch Half CCITT V QAM A or S Full CCITT V.33 14,400 QAM Synch Full Rev 2.0 Sys MFG Training/Employee Development

PC Peripherals for Technicians

Similar presentations

Presentation on theme: "PC Peripherals for Technicians"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

PC Peripherals for Technicians

Similar presentations

Presentation on theme: "PC Peripherals for Technicians"— Presentation transcript:

Similar presentations

About project

Feedback