please dont rip this site


by Jinx

DOGM are a COG (chip on glass) style of LCD which is an attractive
alternative to the standard alphanumeric display. The space behind
the display and its transparency, as well as the functionality of the
controller, make options available to the user not possible with self-
contained modules

This page is here to demonstrate initialisation with a PIC, as much of
the material out there purporting to do this is confused, misleading
or just wrong

Manufacturer's site

At this time, April 2011, DOGM LCDs are in stock at Mouser

Unlit, daylight

lit, diffused white LEDs

Tested on PIC 18F2520, 39.3216MHz (9.8304MHz PLL)

LCD Vdd = 5V, 8-bit parallel mode


line1    macro
         movlw  0x00+0x80        ;line 1, column 0
         call   writec

line2    macro
         movlw  0x40+0x80        ;line 2, column 0
         call   writec

display  macro   var             ;load TBLPTR with string address
         movlw   upper(var)
         movwf   tblptru
         movlw   high(var)
         movwf   tblptrh
         movlw   low(var)
         movwf   tblptrl
         call    get_txt         ;get characters, print

;PortC 0-7 - LCD data

#define  rs       latb,1      ;RS
#define  rw       latb,2      ;R/W
#define  en       latb,3      ;Enable

;example definitions

function1 = 0x39
function2 = 0x38
bias      = 0x1c
power     = 0x52
follower  = 0x69
contrast  = 0x74
disp_on   = 0x0c
disp_off  = 0x08
clear     = 0x01
entry     = 0x06

crsr_on   = 0x0f
crsr_off  = 0x0c
ddram     = 0x80
cgram     = 0x40

strings   = 0x400                ;display string storage address

         bcf     en
         bcf     rw
         bcf     rs
         call    ms100           ;> 18ms delay

         call    lcd_init

         display m1              ;show Line1 text
         display m2              ;show Line2 text

;        Initialise LCD screen (8-bit, 5V)

;The 162 initialisation sequence found on page 7 of
;Electronic Assembly's product guide

;is substantially correct, although it doesn't contain
;other required information found in the ST7036 datasheet
;The initialisation sequences and code examples in
;the ST7036 datasheet, however, are just plain rubbish
;You should have it though

lcd_init movlw  function1        ;must use this sequence
         call   writec

         movlw  power
         call   writec
         movlw  contrast
         call   writec
         movlw  bias
         call   writec
         movlw  follower
         call   writec

         movlw  function2
         call   writec

         movlw  disp_on
         call   writec
         movlw  clear
         call   writec
         call   ms01
         call   ms01
         movlw  entry
         call   writec


writec   bcf    rs
         bcf    rw
         bsf    en
         movwf  d_temp           ;temp if W over-written by delay
         call   us100            ;> 96us delay
         movfw  d_temp
         movwf  latc
         bcf    en
         call   us100            ;> 78us delay

writed   bsf    rs
         bcf    rw
         bsf    en
         movwf  latc
         bcf    en
         call   us30             ;> 15us delay

;        Fetch string for LCD

; LCD text strings

get_txt  movfw   tablat       ;get characters until
         btfsc   wreg,7       ;W > 0x7f (ie FF terminator)
         call    writed       ;print W
         bra     get_txt

;        LCD text strings

 org strings

m1       db "Gettin' it done",0xff
m2       db "WWW.PICLIST.COM",0xff

In this analyser shot of the initialisation sequence, note that Busy (D7) is useless
for interrogation. As soon as R/W goes low, Busy goes high, and remains there.

writec has two 100us delays that must be done. The completion time for writed
is quite short, around 20us, so a wait delay would probably be practical for most
software. If not, the user will have to make sure enough time has elapsed before
attempting to write more data

So far I've not been able to get a double-height display that looks like the one
in the datasheet. As far as I can tell, there is no central line of pixels to fill the
gap. All 16 rows are accounted for. If this is true, double height would be of
limited use. please if you find any missing pixels or have
the command values to display double height as seen in the datasheet. The double
height datasheet illustration, by the way, uses an undocumented "S" and is not
italicised, so make of that what you will

Serving suggestions

lit, red cellophane

lit, green wine bottle

lit, printed paper insert (transparency would be much better)

lit, pink/purple cellophane

backlight jig, using dimmable 3 x 1W white LEDs and opalescent acrylic


This PCB can be wired to suit any of the 6 options in the dog-me.pdf. It's the
pattern I've used for toner transfer. Make sure that the solder bridge gaps are
open after etching, or amend the diagram to suit your hard-wired configuration

EA have an Eagle library, ea.lbr, in their Downloads section

The cutout can be removed if you want the lighting to be further back, which
will help the light spread and improve evenness

Note that COG displays are fragile and trying to remove one from a PCB could
cause it to be damaged

Copied with permission from:

See also:

file: /Techref/microchip/io/dev/lcd/DOGM.htm, 7KB, , updated: 2011/4/22 17:44, local time: 2024/4/23 14:16,

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