EET 2261 Unit 12
Controlling LCD and Keypad
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Read Almy, Appendix E.
Homework #12 and Lab #12 due next
week.
Quiz next week.
Liquid-Crystal Display
•The Dragon12 board has a liquid-crystal
display (LCD) module that lets the programmer
display text messages to the user.
•Datasheet for SHZJ-A162A LCD module
•The LCD module contains an LCD panel and
an LCD microcontroller that has its own
memory distinct from the HCS12’s memory.
This microcontroller handles most of the work
of displaying characters on the LCD panel.
•Datasheet for S6A0069 LCD controller
Dimensions of Our LCD Panel
•The S6A0069 can control a variety of LCD
panels. Variations include:
•Number of lines (1 or 2)
•Number of characters per line (16, 20, 40… )
•Size of matrix of dots that make up a character
(5x8, 5x11).
•Our panel has two lines of 16 characters per
line, with a 5x8 matrix of dots for each
character.
5x8 Dot Matrix Example
•The figure to the right
shows which of the dots in
the 5x8 matrix are lit to
display an A.
•Normally we won’t have to worry about this
level of detail. We’ll just send the ASCII code
for A to the LCD module, and it will take care of
lighting up the correct dots.
•But we do have the ability to create custom
characters if we wish.
List of LCD Commands
•
See Table 7 on page 16 of the S6A0069
datasheet for a list of all commands that the
LCD recognizes.
•
Most of these commands are used for
initialization, such as specifying:
• Whether our LCD panel has 1 line or 2.
• Whether it displays characters with a 5x8
dot matrix or a 5x11 matrix.
• Whether we want the cursor to be visible.
• Whether we want the cursor to blink.
Typical Initialization Code
I/O Pins on the LCD Module
•Figure and table
from the SHZJA162A datasheet.
LCD Connections on Dragon12
•LCD is connected to
the HCS12’s Port K.
•The LCD’s R/W pin
is permanently
grounded (through
jumper J5), placing
the LCD permanently
in write mode.
Figure from page 4 of the
Dragon12 schematic diagrams.
•Only 4 of the 8 bits on the LCD’s data bus
are connected to the HCS12. This is a
common practice, to save pins.
Command or Data?
•We can send two kinds of things to the LCD
module:
1. Commands, such as:
•Clear the display.
•Move cursor to the 4th position on line 1.
•Make the cursor blink.
2. Data, which is ASCII code for text to be
displayed, such as “Rock on!”
•
We must set the RS (Register Select) bit
LOW when we’re sending a command,
and set it HIGH when we’re sending data.
Executing the Command or Data
•We must hold the EN line (which connects to
the LCD module’s E pin) LOW most of the
time.
•After we’ve set the RS line to its correct level,
and put a command or data on the bus, we
must send a brief LOW-to-HIGH-to-LOW
pulse on the EN line. This pulse is what
actually tells the LCD module to perform the
action we’ve requested.
Steps for Sending a Command to
the LCD
•
To send a command (such as Clear
Screen) to the LCD, a program must:
1. Store the upper nibble of the command
byte to Port K bits 2-5, and set Port K bit
0 LOW. (Bit 0 tells whether we’re
sending a command or data.)
2. Pulse Port K bit 1 HIGH-then-LOW.
3. Store the lower nibble of the command
byte to Port K bits 2-5 , and set Port K bit
0 LOW.
4. Pulse Port K bit 1 HIGH-then-LOW.
Sample Code For Sending a
Command (Assumes command byte is in Accumulator A)
Steps for Sending Data to the LCD
•
To send data (such as the character H) to
the LCD, a program must:
1. Store the upper nibble of the data byte to
Port K bits 2-5, and set Port K bit 0
HIGH.
2. Pulse Port K bit 1 HIGH-then-LOW.
3. Store the lower nibble of the data byte to
Port K bits 2-5 , and set Port K bit 0
HIGH.
4. Pulse Port K bit 1 HIGH-then-LOW.
Code For Sending Data
•
You can easily modify the SendCommand
subroutine (on the slide before the previous
one) to create a SendData subroutine.
Sample Code for Displaying a
Character
•
Assuming we’ve set everything up correctly
with our initialization code, we can send text
to be displayed. The code below positions
the cursor and then sends an H.
ASCII Code
•
As defined in the 1960’s, ASCII code is a 7-bit
code, whose values range from $0 to $7F (or
%0111 1111). Thus it contains the codes for
128 characters, as shown on page 375 of our
textbook.
•
The first 32 codes (from $0 to $1F) and the
last code ($7F) were originally defined as
non-printable control codes to control
Teletype equipment. Most of these control
codes are obsolete in today’s world.
Extending the ASCII Code
•
Since the 1960’s, manufacturers have
extended the ASCII code in two ways:
1. By redefining some of the now-obsolete
control codes.
2. By extending the code from 7 bits to 8 bits,
thus allowing for an additional 128
characters.
•
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One such widely used extension is the one
that IBM used on its PCs: see
http://en.wikipedia.org/wiki/Code_page_437.
Our LCD module assigns different
characters to these codes.
Our LCD Module’s Character Set
•
On our LCD module:
• Codes $00 through $07 are reserved for
user-defined characters.
• Codes $08 through $1F are unused.
• Most of the codes in the range $20 through
$7F agree with the standard ASCII set.
• Codes $80 through $9F are unused.
• Codes $A0 through $FF produce special
characters.
Dragon12-Plus2 Keypad
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Our Dragon12-Plus2 board has a
keypad with 16 switches (or keys).
The switches are arranged in a 4-by-4
matrix.
Each row of this matrix is attached to
one of the Port A pins PA4 to PA7.
Each column of the matrix is attached
to one of the Port A pins PA0 to PA3.
See diagram on next slide.
Dragon12 Keypad Connections
Figure from p. 26 of Dragon12-Plus2 manual.
Different from the Textbook’s Keypad
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Caution: the keypad connections on
our Dragon12-Plus2 board are different
from the connections assumed in the
textbook’s discussion (as shown in the
figures on page 340 of the textbook).
Therefore, while the general principles
of the book’s discussion do apply to our
keypad, the details are different.
Configuring the Keypad
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To use the keypad, we must first
configure it:
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Configure Port A pins 0 to 3 as outputs.
(These are the pins connected to the
keypad columns.)
Configure Port A pins 4 to 7 as inputs.
(These are the pins connected to the
keypad rows.)
Identifying Which Key is Pressed
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General idea: Make one column output
HIGH at a time (while other columns
are LOW), and then check each row
input to see if any of them are HIGH. If
it is, then we know which key is being
pressed.
See next slide for modified version of
keyboard scan routine from p. 27 of
Dragon12 manual.
Keyboard Scan Routine
Modified from
p. 27 of Dragon12
manual.
Set PA0 high and PA1, PA2, PA3 low, and then test PA4-PA7.
If no key is pressed, PA4-PA7 remain low.
If PA7 = high, then key 12 is pressed.
If PA6 = high, then key 8 is pressed.
If PA5 = high, then key 4 is pressed.
If PA4 = high, then key 0 is pressed.
Set PA1 high and PA0, PA2, PA3 low, and then test PA4-PA7.
If no key is pressed, PA4-PA7 remain low.
If PA7 = high, then key 13 is pressed.
If PA6 = high, then key 9 is pressed.
If PA5 = high, then key 5 is pressed.
If PA4 = high, then key 1 is pressed.
Set PA2 high and PA0, PA1, PA3 low, and then test PA4-PA7.
If no key is pressed, PA4-PA7 remain low.
If PA7 = high, then key 14 is pressed.
If PA6 = high, then key 10 is pressed.
If PA5 = high, then key 6 is pressed.
If PA4 = high, then key 2 is pressed.
Set PA3 high and PA0, PA1, PA2 low, and then test PA4-PA7.
If no key is pressed, PA4-PA7 remain low.
If PA7 = high, then key 15 is pressed.
If PA6 = high, then key 11 is pressed.
If PA5 = high, then key 7 is pressed.
If PA4 = high, then key 3 is pressed.
Code That Implements the Keyboard
Scan Routine
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Download the code from
http://people.sinclair.edu/nickreeder/eet2261/
labs/lab12KeypadNumberToLEDs.txt .
Key Numbers Versus Key Labels
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On previous slides we’ve been referring to
keys by their numbers, starting with key #0 in
upper left corner of keypad and ending with
key #15 in lower right corner.
Don’t confuse these
key numbers with the
labels on the keys,
which are shown at
right.