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89C4051 Newbie needs help

Hi,

I have connected a 16X2 LCD to my 4051 on a breadboard. The P1 is connected to the data lines of the LCD in 8 bit format. RW is grounded, RS to P3.0 and E to P3.1.

I wrote a short program to send the bytes 38h, 38h, 06, 0Fh, 01 to P1 and on each byte I pulsed the E line H then L. But nothing happened on the LCD. I attached the software at below. Can anyone see what's wrong with it?

; MYLCD.asm written on 030822 ; ; P1 as LCD data and p3.0 & p3.1 as rs & e ; $mod51

LCD_data set p1 LCD_RS equ 0b0h ;p3.0 LCD_E equ 0b1h ;p3.1 ; config equ 38h ;8 bit data, 2 lines, 5x7 matrix entrymode equ 6 ;inc cursor, do not shift display combncur equ 0fh clrdsp equ 1 ; org 0000h ; reset: jmp start ; org 0100h ; start: mov p1,#0 ;set p1 dir out clr LCD_rs ;set rs L clr LCD_E ;set e L mov r0,#config ;#38 call wrlcd ;send it to LCD mov r0,#config ;#38 call wrlcd mov r0,#entrymode ;#06 call wrlcd mov r0,#combncur ;#0f call wrlcd mov r0,#clrdsp ;#01 call wrlcd loop: jmp loop ; wrlcd: push acc mov a,r0 mov p1,a clr lcd_rs ;make sure it is L setb lcd_e ;pulse lcd_e clr lcd_e call wait ;wait for 65ms pop acc ret wait: mov r2,#0ffh ;delay for a while wait0: mov r3,#0ffh wait1: nop djnz r3,wait1 nop djnz r2,wait0 ret end ;end of program

Allen

------ The next war will determine NOT who is right BUT what is left.

Reply to
Allen Bong
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"Allen Bong" wrote

Sorry, haven't really got the inclination to check your code for you - but you might want to check that you have pullups on P1.0 and P1.1 (common trap with this micro)

You also need to monitor busy on most LCD's, and transmit when the LCD is not busy, and you usually need to go through an initialisation sequence for the LCD. Good Luck.

Regards Steve

formatting link

Reply to
Apollo

Kind of looks ok to me. What clock speed is your CPU running at? You might want to check to make sure you're holding E high for a long enough period with an oscilloscope. Is your delay really 65ms (milliseconds) or did you mean us (microseconds). If the former, then it seems excessive (but wouldn't hurt talking to the LCD). If the latter, then it's too short for the 01 command (82us to 1.64ms in the datasheet I'm looking at).

Reply to
Gary Kato

did you set the contrast? any "black" lines visible? you only send "clrdsp" command. how about one data byte? rw

Reply to
Rein Wiehler

connected

P3.0

and on

LCD. I

No, is 10K ohms OK for this purpose? What about p3.0 and p3.1? Do they also need pullups?

No, I didn't monitor the busy as I gave it ample time (65ms) to do its job.

Reply to
Allen Bong

want

an

I am using 12MHz xtal and as the book says, 1 instruction per uS so the wait loop should be greater than 65 mili-seconds as I looped it 255 X 255 times with an NOP in between.

I have connected the LCD display to an New Micro NMIY-0031 board and use the O (output byte) to send the sequence one byte at a time and the lcd displayed a flashing cursor after the 01 (clrdsp) byte. SO my LCD is definitely good.

Allen

Reply to
Allen Bong

"Allen Bong" wrote

Yes, that should be just great. If the LCD has pullups then they wouldn't be required - but I don't think many LCDs have pullups.

No, I think it is more just P1.0 and P1.1 because they can also be the comparator lines. They are OC.

Yes, ofcourse - sorry, I didn't look properly. Hopefully with this and a contrast pot it will all spring into life. If your LCD is a high temp one, be careful - some of those need a slight negative voltage on the contrast pot. Either way, you should be able to wind it around until the display goes a bit black, then back it off.

Regards Steve

formatting link

Reply to
Steve

[snip]

Only if you sent the appropriate contol bytes to turn the cursor on (& select whether block or underline) and tell it to flash!!

There is not a lot of intelligence in these displays - you have to tell them to do absolutely *everything*

HTH

Chris

Reply to
Chris Hoffmann

Thanks to Steve & Rein,

My 16X2 LCD is finally working. I am going to add in the text to display and later convert my software to work in 4 bit mode and make use of the RW lines to detect BUSY state. Without your help it would have meant another 3 weeks' hard work for me. Thanks again.

Allen

P1

job.

Reply to
Allen Bong

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