EE 316 Computer Engineering Junior Lab Serial Ports, LCD Displays & PROMs

Topics PC Serial Ports Liquid Crystal Display Modules

PC's Serial Ports ● PC's Serial port (RS-232c interface) is also known as the communication (COM)port. ● The serial port transmits a byte of data by sending 8 bits separately. It adds a start bit, a stop bit and if desired, a parity bit. ● COM ports are bi-directional. Serial ports use a special controller chip known as the Universal Asynchronous Receiver/Transmitter (UART), to function correctly. ● Used to connect to Modems, some printers and digital cameras. Ref:

PC's Serial Port, contd. ● Serial cables can be longer than parallel cables. ● The RS-232c data uses -3 to -12 V to represent a 1 (called Mark) and +3 to +12 to represent a Logical '0' (called Space). ● Serial data must be converted to TTL/CMOS level for digital circuits.

PC's Serial Port, contd. ● One can use the RS-232 drivers and recievers to transform the RS-232 level to TTL/CMOS level.

UARTs Universal Asynchronous Receiver/Transmitter ➔ To use the serial data in digital applications, we need to convert the TTL/CMOS serial data into parallel data using UARTs. ➔ Popular UARTs: 16550, & 8250 series ➔ We will use a CMOS based UART: HD Read the data sheet carefully before using. ➔ UARTs use a clock with is 16 times the baud rate of the serial port.

UART Timing & Control Issues

Interfacing a digital system with a PC (another digital system) PC and its UART and level converter MAXIM 233UART

DB9_Ribbon_Cable_Header

Liquid Crystal Display (LCD) modules Majority of the pixel-based alphanumeric LCD module uses the Hitachi HD44780 LCD controller chip. Makers are: Densitron, Epson, Hewlett Packard, Optrex, or Sharp. Most have 16, 20, 24, 32, or 40 characters by 1, 2, or 4 lines. The LCD module we will use has a single line of 20 characters. Each character is made of 5x7 dot matrix For more info: /

LCD Display To use these LCD module, you have follow the timing requirement very precisely. Pay attention to these times Important times

LCD Initialization Before you use the LCD, you need to initialize the LCD with a very precise sequence of instructions. Follow the intialization very accurately  Need to generate a sequence of 8-bit instructions with a minimum timing delay between two instructions  each instruction requires multiple steps raise the enable signal ‘E’, apply data or instruction, lower ‘E’, hold data or instruction  You may store these values in a PROM and apply to the LCD with correct times between two instructions.

LCD Initialization Contd. In this example at the end of the initialization the LCD is asked to return cursor to the home postion and clear previous display. The LCD is then readied for display data (DD) input. The ASCII code for capital “D” is then sent to the LCD module Initialization begins here Initialization ends here LCD is ready for Display data input ASCII 0x44 = D

ASCII code

PROM Read only memory  32K x 8 bits or 64K x 8 bits, etc.  Erasable with UV exposure (15-20 mins)  For 32K, 10 address Pins  8 data Pins  Pin named Vpp used for progrmming  Chip enable  Read enable

Power-On Reset In most sequential circuits (i.e., circuits that have FF, latch, or counters, memories), the initial state may not be known after the power is turned on. Use a RC circuit for the Reset or Clear the FFs. Choose the RC values for correct timing.

References