RS232 Serial and Parallel Interfaces

What Is a Interface? The point of interaction or communication between a computer and any other entity, such as a printer or human operator.

Types of Interfaces RS232 nine pin serial port Parallel port USB port SCSI port Animated, when the slide is done, it leaves the top three highlighted IEEE 1394 PCI cards, etc.

RS232 9pin Serial Port Has existed for approximately 20 years RS232 stands for Recommended Standard 232 C Used mostly for devices that transmit or receive small amounts of data RS232 stands for Recommended Standard 232 C and is an electrical data communications standard published by the Electronic Industries Association (EIA).(D. Lawyer, Serial HOWTO, 2001) Devices like: PDA cradles, barcode scanners, some printers, industrial applications, external modems. Basically things that process data slower then 115 kbps.

What Does Serial Mean? The name 'serial' comes from the way that a serial port 'serializes' data. That is, it takes a byte of data and transmits the 8 bits in the byte one bit at a time.

How Does It Work? 01101110 1 1 1 1 1 1 1 1 1 Animated slide, explain how it applies to all eight bits, explain that the device or computer translate a voltage level into “0” and “1”. That the device and computer process information in parallel.

Facts About the RS232 Port Data throughput rate of 115Kbps Most computers have one or two RS232 ports built in to the motherboard More ports can be added by adding an adapter card to the computer; These cards again add one or two extra ports All RS232 devices need to have a device driver installed on the computer to operate correctly 1> rate given for SPP, ESP and SESP are around 460kb/s 2> port multipliers can be added, but are costly and complex, only special applications like industrial sensing or data aquasition. 3> Usually comes with the device.

RS232 Summary In general the RS232 interface is a fairly slow and complex way to connect devices to a computer. The lack of protocol and configuration standards for the interface means that users must manually configure the port for each new device added.

The Parallel Port Developed by IBM to connect PC to a printer Probably most common form of port used IBM decided not to use the 36-conductor connector that Centronics used on their printers, instead IBM used a 25-conductor connector on the PC. The parallel connector is located on the back of most computers and is a 25-pin D shell female connector (the outside shape of the connector is shape like a capital D and has 25 holes on the inside of the connector). . In 1994 the Institute of Electrical and Electronics Engineers (IEEE) developed IEEE-1284 , a standard for parallel ports that included both the EPP and ECP specifications. The IEEE-1284 standard is the standard that governs today's parallel ports. (J. Tyson, How Parallel Ports Work, n.d.)

Types Parallel Ports Uni- Directional Bi-Directional

What Does Parallel Mean? Of or relating to the simultaneous transmission of all the bits of a byte over separate wires: a parallel part; a parallel printer.

How Does It Work? 01101110 01101110 01101110 01101110 01101110 01101110 01101110 Animated, click to watch a byte of data move from the computer to the printer. 01101110

Facts About a Parallel Port The specification allows up to 2Mbps The specification allows up to a 10 meter cable Most PC’s come with one or two parallel ports, as with a serial port, more can be added if required (1 or 2 only) All devices require a device driver which is usually provided by device manufacturer The IEEE-1284 standard specifies data throughput rate of up to 2Mbps and cable lengths of up to 10 meters. Practical data throughput rate and cable lengths would depend on the configuration of devices connected to the computer. If you are connecting a printer you will not need to set the low level communication parameters (interrupt level, direct memory addresses, and I/O range) you can use the Windows default. Windows also has drivers for many printers built in, making connecting a printer a simple task.   Connecting other devices to the parallel port can be more complicated. Depending on the type of device and the number of devices you are connecting to a single parallel port you may have to set the low level communications parameters. For common devices like Zip drives and optical scanners the drivers supplied by the equipment vendor will handle the settings without user intervention.

Parallel Port Pins 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 DB-25 Male Connector

Parallel Port Pin Configuration 1 14 16 17 4 Control Pins 2 3 4 5 6 7 8 9 8 Data Pins 10 11 12 13 15 5 Status Pins 18 19 20 21 22 23 24 25 8 Ground Pins DB-25 Male Connector

Pin Assignment & Descriptions Strobe PC Output Data 0 PC Output Data 1 PC Output Data 2 PC Output Data 3 PC Output Data 4 PC Output Data 5 PC Output Data 6 PC Output Data 7 PC Output ACK (Acknowledgment) PC Input Busy PC Input Paper Empty PC Input Select PC Input Auto Feed PC Output Error PC Input Initialize Printer PC Output Select Input PC Output

Simple LEDs Driving Circuit 10 11 12 13 15 2 3 4 5 6 7 8 9 1 14 16 17 18 19 20 21 22 23 24 25 Anode  100 Ohm Resistance or Deponds on LEDs 3 Volts LEDs  Cathode  Grounding Pins

LEDs Driving Circuit - Example 1 Anode  100 Ohm Resistance or Deponds on LEDs 3 Volts LEDs  Cathode  Grounding Pins

Simple Example Program #include <dos.h> // Include header file #define DATA 0x378 // Base address of Data Pins #define STATUS DATA+1 // Status address of Status Pins #define CONTROL DATA+2 // Control address of Control Pins void main(void) { outportb(DATA, 0x00); // Turn all the LEDs off delay(1000); outportb(DATA, 0x01); // Turn the 1st LED on }