Post by thread:4 Bit LCD HD44780 Interface Code

go to http://www.parallaxinc.com and get the basic stamp manual. It has detailed info on how to talk to this device in 4 bit mode. On Sun, 19 Jul 1998, Taylor Jacob wrote: {Quote hidden}> I am about to start a project for the PIC 16F84 at 10mhz , and I > need to interface with a HD44780 Interface 20x4 LCD screen.. Since I am > using most of the IO Lines on the PIC for other tasks, I can only talk to > the LCD in 4 bit mode (4 io pins for data, 1 for E, 1 for SE, and RS will > tied to ground, since I don't need to read from the LCD..).. > > I was wondering if anyone had already written the code to talk to > the LCD, display characters, etc.. If someone would be so kind as to send > that code to me it would save me a good deal of time.. > > Taylor Jacob >

> go to http://www.parallaxinc.com and get the basic stamp manual. > It has detailed info on how to talk to this device in 4 bit mode. I have the datasheet, I was just wondering if someone already had the code, and wanted to let me have a copy of it, rather than coding it myself, and spending time debugging that code.. > > I am about to start a project for the PIC 16F84 at 10mhz , and I > > need to interface with a HD44780 Interface 20x4 LCD screen.. Since I am > > using most of the IO Lines on the PIC for other tasks, I can only talk to > > the LCD in 4 bit mode (4 io pins for data, 1 for E, 1 for SE, and RS will > > tied to ground, since I don't need to read from the LCD..).. > > > > I was wondering if anyone had already written the code to talk to > > the LCD, display characters, etc.. If someone would be so kind as to send > > that code to me it would save me a good deal of time..

At 21:46 19/07/98 -0400, you wrote: > I am about to start a project for the PIC 16F84 at 10mhz , and I >need to interface with a HD44780 Interface 20x4 LCD screen.. Since I am >using most of the IO Lines on the PIC for other tasks, I can only talk to >the LCD in 4 bit mode (4 io pins for data, 1 for E, 1 for SE, and RS will >tied to ground, since I don't need to read from the LCD..).. You will find ASM file for LCD & 16F84 as well as UMPS project for LCD panel in UMPS directory: UMPSDEMO\EXAMPLES\16C84 UMPS can be downloaded at: http://www.sistudio.com/umps Best regards, Philippe. +--------------------------------------------------------+ | Virtual Micro Design | | Technopole Izarbel, | | 64210 BIDART | | FRANCE | | | | Phone: ++33 559.438.458 Fax: ++33 559.438.401 | | | | E-Mail: spam_OUTp.techerTakeThisOuTidls.izarbel.tm.fr | | URL: http://www.sistudio.com/umps | +--------------------------------------------------------+

Hi Taylor, I don't know what your app is, but I found in mine that time spent setting up the data bits and such became considerable. This is because I have to put text on the screen quickly and the guy who laid out the PCB put the data bits all over the place! I'd recommend keeping the LCD data bits grouped together. All 8-bits in the same port, or 4 bits in D7:4 if 4-bit mode. This keeps code simple and small. I prefer 8-bit mode - repeated spaces are needed often to wipe previous chars. In 8-bit mode you only need to set the data once, and simply strobe it in multiple times. In 4-bit, you have to set up '2' then '0' for each space. I can see how my project could have got 8-bit mode and used less pins, by having pins doing multiple functions. For example, a data line to volume attenuators can be used, since it won't affect the volume unless the strobe for that chip is asserted. There are 7 lines driving channel indicator LEDs and scanning the keyboard. These could also be borrowed if the LEDs can be temporarily disabled (e.g. by 2N7000 FET in the common cathode). Hope these tips help.

At 09:46 PM 7/19/98 -0400, you wrote: > > I was wondering if anyone had already written the code to talk to >the LCD, display characters, etc.. If someone would be so kind as to send >that code to me it would save me a good deal of time.. If you don't mind Parallax (ack!) code, I just got this running. Note that I hooked up the LED backlight to ra2 and ra3. You'll have to adjust 'wait' subroutines, this code works on 16mhz 16F84. :-) 2x16 Display. ; PROGRAM: LCD.SRC ; Taken from Parallax PIC Application Note: Driving a Liquid Crystal Display ; DA - July 9,1998 device pic16c84,hs_osc,wdt_off,protect_off RS = RA.1 ;REGISTERSELECT - PIN 6 H=DATA L=INSTRUCTION E = RA.0 ;ENABLE - PIN 5 data = RB ;Data to LCD LCDLED1 = RA.2 LCDLED2 = RA.3 count = 9 ;Number of characters in demo string. char_cnt = 64 ;Number of bytes in custom character ;definition line1 = 10000001b line2 = 11000001b ; Declare constants for common LCD instructions. To perform the functions ; listed below, clear bit RS and send #constant to the display. Remember to set ; RS again before sending characters to the LCD. clear = 1 ;Clears the display (fills with blanks) home = 2 ;Returns display to the home position. shift_l = 24 ;Shifts display to the left. shift_r = 28 ;Shifts display to the right. crsr_l = 16 ;Moves cursor to the left. crsr_r = 20 ;Moves cursor to the right. blink_c = 11 ;Blinks whole character to indicate ;cursor position. no_crsr = 8 ;Turns off the cursor. ; Set RAM origin above special registers, declare variables, and set code ; origin. org 0CH temp ds 1 ;Temporary counter. temp2 ds 1 counter ds 1 ;Index variable. output ds 1 ;data to send output2 ds 1 ;data to send org 0 start mov ra, #01100b mov rb, #0 mov !ra,#0h ;Set control lines to output mov !rb,#0h ;Set data lines to output call long_wait ;Initialize LCD: set 4-bit, 1-line ;interface data lenght = 4 ;lines = 2 mov output,#0011b call Iout1 mov output,#0010b call Iout1 ; clear display mov output,#00000001b call Iout ;entry mode select mov output,#00011000b call Iout ; turn on mov output, #00001111b call Iout ; jmp send_msg ; CREATE CUSTOM CHARACTERS mov output,#01000000b call Iout mov counter, #0 :stuff mov w, counter call my_chars ;Get next byte. mov output, w ;Write byte to CG RAM. call Dout inc counter cjb counter, #char_cnt, :stuff clr counter send_msg mov output, #line1 ;Address ? of DD RAM. call Iout :loop mov output,counter call Dout inc counter sb counter.4 jmp :loop mov output,#line2 call Iout :loop2 mov output,counter call Dout inc counter snb counter.4 jmp :loop2 jmp send_msg Iout1 call long_wait ; go slow... clrb RS ;instruction register mov rb,output ;send command setb E clrb E ret Iout call wait ; go slow... clrb RS ;instruction register jmp Dout2 ;Data out Dout setb RS ;data register Dout2 call wait ;go slow... swap output mov rb,output ;send MSNybble command setb E clrb E swap output mov rb,output ;send LSNybble command setb E clrb E ret long_wait mov temp2,#35 goto wait2 wait mov temp2,#30 wait2 djnz temp,$ djnz temp2,wait2 ret msg jmp pc+w retw 'x','D','o','m','1','2','3','4','5','6','7' my_chars jmp pc+w ;Table of data for custom 'backwards' ;characters. retw 31,31,0,0,0,0,31,31 ; lines retw 31,31,31,0,0,31,31,31 ; lines retw 31,3,3,31,31,3,3,31 ; lines retw 0,0,31,31,31,31,0,0 ; lines retw 31,31,7,3,3,7,31,31 ; lines retw 31,31,3,1,1,3,31,31 ; lines retw 31,31,3,3,3,3,31,31 ; lines retw 31,31,17,17,17,17,31,31 ; lines