G
Gauntlet
Guest
I recently purchased a 20x4 backlit LCD from a surplus shop. It seems
to be in good working order, however, I am having difficulty getting
the last character in the 3rd and 4th lines to display properly.
The controller is a legit HD44780A00, and there are four HD44100H ICs
on it as well. Unfortunately I don't know the manufacturer of the
module, but it has "V0020240 Rev. B" silkscreened on the back.
I'm using the 8-bit interfacing method, connecting the display to the
dedicated LCD port on my brand-new Rev.5 8051 devkit from pjrc.com. I
took the website-provided 2x15 display code and modified it to output
a single character to a specific LCD address, allowing me to randomly
step through memory to try and determine the memory map for the
device.
Rows 1 and 2 work as expected:
Row 1: 01h - 14h (20 chars)
Row 2: 41h - 54h (20 chars)
Rows 3 and 4 are problematic:
Row 3: 15h - 27h (19 chars) - 28h does not work
Row 4: 55h - 67h (19 chars) - 68h does not work.
Oddly, 40h or 28h puts a character at the end of the 4th row, and I
need to use 6Ah to get something at the end of the 3rd row.
Could this be an oddball hardware problem, or am I missing something?
Here's the code, if that may help:
..equ locat, 0xF300 ;Location for this program
..equ lcd_command_wr, 0xFE00
..equ lcd_status_rd, 0xFE01
..equ lcd_data_wr, 0xFE02
..equ lcd_data_rd, 0xFE03
..equ esc, 0x003E ;paulmon2's check for esc key
..org locat
..db 0xA5,0xE5,0xE0,0xA5 ;signiture bytes
..db 35,255,0,0 ;id (35=prog)
..db 0,0,0,0 ;prompt code vector
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;user defined
..db 255,255,255,255 ;length and checksum (255=unused)
..db "4x20 LCD Test",0 ;max 31 characters, plus the zero
..org locat+64 ;executable code begins here
startup:
..equ cout, 0x0030 ; cout: print byte in accumulator
to serial port
..equ cin, 0x0032 ; cin: get a character from the
serial port (blocking)
..equ phex, 0x0034 ; phex: print accumulator value
as 2-digit hex
..equ phex16, 0x0036 ; phex16: print DPTR value as
4-digit hex
..equ pstr, 0x0038 ; pstr: print string pointed to
by DPTR
..equ newline, 0x0048 ; newline: send cr+lf to serial port
..equ ghex, 0x003A ; ghex: read ascii, store in acc.
as hex
..equ lcd_clear_cmd, 0x01 ;clears display
..equ lcd_home_cmd, 0x02 ;put cursor at home position
..equ lcd_on_cmd, 0x0C ;turn on display (cursor off)
..equ lcd_left_move_cmd, 0x10
..equ lcd_right_move_cmd, 0x14
..equ lcd_left_shift_cmd, 0x18
..equ lcd_right_shift_cmd, 0x1C
..equ lcd_config_cmd, 0x38 ;configure, 8 bit interface, 2
lines, 5x7 digits
main_loop:
lcd_init:
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_config_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_clear_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_on_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_left_shift_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #0x81
movx @dptr, a
begin:
mov dptr, #mesg_start
lcall pstr
getaddr:
lcall ghex
lcall newline
jc quit
setaddr:
orl a, #0x80 ; msb set for set DD RAM
address
mov dptr, #lcd_command_wr ; set LCD write port
movx @dptr, a ; and output character to LCD
sendstr:
mov dptr, #mesg1
acall lcd_pstr
quit:
ljmp 0
; mesg_start: data sent to serial port at program initialization
mesg_start:
.db "Enter screen address to try: ",0
; mesg1 : data sent to LCD during main loop
mesg1:
.db "+",0
lcd_pstr:
clr a
movc a, @a+dptr
inc dptr
jz lcd_pstr_end
push dpl
push dph
acall lcd_cout
pop dph
pop dpl
sjmp lcd_pstr
lcd_pstr_end:
ret
lcd_cout:
push acc
acall lcd_busy
mov dptr, #lcd_data_wr
pop acc
movx @dptr, a
ret
lcd_busy:
mov dptr, #lcd_status_rd
movx a, @dptr
jb acc.7, lcd_busy
ret
to be in good working order, however, I am having difficulty getting
the last character in the 3rd and 4th lines to display properly.
The controller is a legit HD44780A00, and there are four HD44100H ICs
on it as well. Unfortunately I don't know the manufacturer of the
module, but it has "V0020240 Rev. B" silkscreened on the back.
I'm using the 8-bit interfacing method, connecting the display to the
dedicated LCD port on my brand-new Rev.5 8051 devkit from pjrc.com. I
took the website-provided 2x15 display code and modified it to output
a single character to a specific LCD address, allowing me to randomly
step through memory to try and determine the memory map for the
device.
Rows 1 and 2 work as expected:
Row 1: 01h - 14h (20 chars)
Row 2: 41h - 54h (20 chars)
Rows 3 and 4 are problematic:
Row 3: 15h - 27h (19 chars) - 28h does not work
Row 4: 55h - 67h (19 chars) - 68h does not work.
Oddly, 40h or 28h puts a character at the end of the 4th row, and I
need to use 6Ah to get something at the end of the 3rd row.
Could this be an oddball hardware problem, or am I missing something?
Here's the code, if that may help:
..equ locat, 0xF300 ;Location for this program
..equ lcd_command_wr, 0xFE00
..equ lcd_status_rd, 0xFE01
..equ lcd_data_wr, 0xFE02
..equ lcd_data_rd, 0xFE03
..equ esc, 0x003E ;paulmon2's check for esc key
..org locat
..db 0xA5,0xE5,0xE0,0xA5 ;signiture bytes
..db 35,255,0,0 ;id (35=prog)
..db 0,0,0,0 ;prompt code vector
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;reserved
..db 0,0,0,0 ;user defined
..db 255,255,255,255 ;length and checksum (255=unused)
..db "4x20 LCD Test",0 ;max 31 characters, plus the zero
..org locat+64 ;executable code begins here
startup:
..equ cout, 0x0030 ; cout: print byte in accumulator
to serial port
..equ cin, 0x0032 ; cin: get a character from the
serial port (blocking)
..equ phex, 0x0034 ; phex: print accumulator value
as 2-digit hex
..equ phex16, 0x0036 ; phex16: print DPTR value as
4-digit hex
..equ pstr, 0x0038 ; pstr: print string pointed to
by DPTR
..equ newline, 0x0048 ; newline: send cr+lf to serial port
..equ ghex, 0x003A ; ghex: read ascii, store in acc.
as hex
..equ lcd_clear_cmd, 0x01 ;clears display
..equ lcd_home_cmd, 0x02 ;put cursor at home position
..equ lcd_on_cmd, 0x0C ;turn on display (cursor off)
..equ lcd_left_move_cmd, 0x10
..equ lcd_right_move_cmd, 0x14
..equ lcd_left_shift_cmd, 0x18
..equ lcd_right_shift_cmd, 0x1C
..equ lcd_config_cmd, 0x38 ;configure, 8 bit interface, 2
lines, 5x7 digits
main_loop:
lcd_init:
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_config_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_clear_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_on_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #lcd_left_shift_cmd
movx @dptr, a
lcall lcd_busy
mov dptr, #lcd_command_wr
mov a, #0x81
movx @dptr, a
begin:
mov dptr, #mesg_start
lcall pstr
getaddr:
lcall ghex
lcall newline
jc quit
setaddr:
orl a, #0x80 ; msb set for set DD RAM
address
mov dptr, #lcd_command_wr ; set LCD write port
movx @dptr, a ; and output character to LCD
sendstr:
mov dptr, #mesg1
acall lcd_pstr
quit:
ljmp 0
; mesg_start: data sent to serial port at program initialization
mesg_start:
.db "Enter screen address to try: ",0
; mesg1 : data sent to LCD during main loop
mesg1:
.db "+",0
lcd_pstr:
clr a
movc a, @a+dptr
inc dptr
jz lcd_pstr_end
push dpl
push dph
acall lcd_cout
pop dph
pop dpl
sjmp lcd_pstr
lcd_pstr_end:
ret
lcd_cout:
push acc
acall lcd_busy
mov dptr, #lcd_data_wr
pop acc
movx @dptr, a
ret
lcd_busy:
mov dptr, #lcd_status_rd
movx a, @dptr
jb acc.7, lcd_busy
ret