ACE KIT Excercise EX20.c which uses the keypad and the lcd.

JimB · Posted: Sun Sep 18, 2005 5:14 pm

I have read all (well maybe not all) the comments regarding the lcd and keypad from other users, but no one seems to be using the ACE KIT. I have gone through many of the excercises but this one has me stymied.
The keypad connector is connected to Port D and the lcd is connected to the port D LCD header as instructed in the documentation. The lcd lights but there is nothing displayed.
Other posts have mentioned the need for pullup resistors but in this excercise the lcd is providing that requirement.
If anyone has gone through this successfully please send me a tip or two.
I have a little concern since the excercise document appears to not be in its final configuration. Mine has several of the Figures blacked out, so I am wondering if it is going to have another pass through the editing process.

Thanks,
JimB

The code follows;

#include <16f877A.h>
#fuses HS, NOWDT, NOPROTECT, NOLVP
#use delay(clock=20000000)

#include <lcd.c>
#include <kbd.c>

void main() {
char k;

lcd_init();
kbd_init();

lcd_putc("\fReady....\n");

while (TRUE) {
k=kbd_getc();
if(k!=0)
if(k=='*')
lcd_putc('\f');
else
lcd_putc(k);
}
}

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

sseidman · Joined: 14 Mar 2005 Posts: 159

As I recall, the LCD port in the ACE kit works fine "out of the box". There are two possible places where you can plug it it, port B, or port D. If you use the keypad as well, you must use port B. Make sure the driver file is talking to the correct port.

JimB · Posted: Mon Sep 19, 2005 7:47 pm

After looking around here, the forum, for similar problems, I read the kbd.c and found the statement about needing pullup resistors on the keypad unless the lcd is attached. See next two lines taken directly from the kbd.c file.

// Make sure the port used has pull-up resistors (or the LCD) on
// the column pins

So from this statement I am led to believe that having the keypad and the lcd on the same port was intentional. I will try moving it to the B port and see what happens.
I hope that CCS didn't make a mistake regarding this. I know that they sometimes leave out little tidbits of information.

JimB · Posted: Mon Sep 19, 2005 11:39 pm

Moved the lcd to port B and removed comment lines to enable use of port B for the lcd. Added the three pullup resistors to the column lines.
Still no go. Anybody have ideas. I am basically parroting the excercise given.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

That comment in the CCS example file is in error. The pull-up
resistors must be on the ROW pins for the kbd.c file.

JimB · Posted: Tue Sep 20, 2005 10:34 pm

I asked CCS support about the problems I was having. Here is the reply that was sent.

*************************************************
"You need pull-ups (or LCD) on COL0, COL1, COL2 (D5-D7)."

"To read the keypad the software will set ROW0 to low, and ROW1,ROW2 and ROW3 to high.
If COL0-COL3 all read high then no key in ROW0 is pressed. The software then sets ROW1
low and the others HIGH. Again if COL0-COL3 are all high nothing is pressed in that row. If
one of the COLx pins reads low then that column and the row that is now low will indicate
the key that is pressed. The software rotates through all rows and then repeats."

AND

"With this kit use port D for both the keypad and LCD. The POT #10
is used to adjust the LCD contrast. From your description I think the
contrast is not set right. On power up you should see a row of black
boxes, when lcd_init is called the screen should clear. You should
then see the text from the printf even before you press any keys."

****************************************************
There was no mention of the pot in the exercise so I need to pursue that avenue now. At least they gave an explanation of how the keypad is read. Now I wish someone would go through the kbd.c and lcd.c and give a narrative explaining what is going on in these two files. Being a beginner I find much of what is presented a little cryptic. It is hard for me to separate the C functions from the other expressions much of the time.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

JimB · Posted: Sat Sep 24, 2005 3:09 am

I reviewed the great reply from PCM Programmer and learned a great deal from that reply. However, I did get the keyboard and lcd to work as CCS advertised in their exercise, i.e. I got them to work correctly placing the lcd and the keypad on port D, without any pullups. What is a little confusing is that without the program running I measured the voltages on the port D pins and found the following.
D0 - low, D1 - +5V, D2 - +5V, D3 - low, D4 - low, D5 - +5V, D6 - low, and D7 - low. The same hold when the program is loaded but no keypad buttons pushed. This implies that two rows and one column is pulled up by the lcd??????
Where is the book that explains all this stuff in detail. Seems like this forum and all the code displayed is becoming my best instructor.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Download the specification for the controller chip used on many
characters LCDs:
http://www.melabs.com/downloads/hd44780u.pdf
Go to page 54, which shows a schematic of the input circuits.
Notice that signals DB0-DB7, R/W, and RS, are labeled with "pull up MOS".
This means they are using a MOSFET to create a weak pullup on those pins.
On page 48, they say the typical pull-up current is 50ua at 3v.
This means the pullups are typically 60K ohms.

While I was searching for the LCD driver document above, I also
found a good appnote from Maxim on keypad interfacing.
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3414
It can also be downloaded as a PDF, at the bottom of the page.