EE 316 Computer Engineering Junior Lab

1
EE 316 Computer Engineering Junior Lab

• LCD modules, PROMs,
• Serial Ports

2
Topics

• Liquid Crystal Display Modules
• Eraseable Progrmmable ROMs
• Serial Ports

3
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 http//www.doc.ic.ac.uk/ih/doc/lcd
/
4
LCD Display

• To use these LCD module, you have follow the
  timing requirement very precisely.

Pay attention to these times
Important times
http//www.mil.ufl.edu/imdl/handouts/lcd-faq.htm
5
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.

6
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 ends here
Initialization begins here
ASCII 0x44 D
LCD is ready for Display data input
7
ASCII code
8
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

9
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.

10
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 http//computer.howstuffworks.com/serial-port
.htm
11
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.

http//www.beyondlogic.org/serial/serial1.htm40
12
PC's Serial Port, contd.

• One can use the RS-232 drivers and recievers to
  transform the RS-232 level to TTL/CMOS level.

http//www.beyondlogic.org/serial/serial1.htm40
13
UARTsUniversal 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, 16450 8250 series
• We will use a CMOS based UART HD-6402. Read the
  data sheet carefully before using.
• UARTs use a clock with is 16 times the baud rate
  of the serial port.

14
UART Timing Control Issues
15
Interfacing a digital system with a PC (another
digital system)
MAXIM 233
UART
PC and its UART and level converter
16
References

• http//www.doc.ic.ac.uk/ih/doc/lcd/
• http//www.mil.ufl.edu/imdl/handouts/lcd-faq.htm
• http//computer.howstuffworks.com/serial-port.htm
• http//www.beyondlogic.org/serial/serial1.htm40