|
Assembly Code Overview: setup
PPI
This first chunk of code of
PPI.asm will setup the PPI.
We have skipped over the first 47
lines of background information.
; Connections
; LCD Data bus (pins #14-#7) connected to Port A of a 8255 with $08
base address
; LCD Enable pin (#6) connected to Port C bit #7
; LCD R/W pin (#5) connected to Port C bit #6
; LCD RS pin (#4) connected to Port C bit #5
; 8255 Port Addresses (base $08)
base .EQU $08
; UART is at address $00 and PPI is at $08.
pAadr .EQU base + 0
; Address of PortA.
pBadr .EQU base + 1 ; Address of PortB.
pCadr .EQU base + 2 ; Address of PortC.
CWRadr .EQU base + 3 ; Address of Control Word Register (CWR).
;8255 Port Configuration
Mode
pAoChoCliBo .EQU $81 ; A out, C high out, C low
in, B out.
pAiChoCliBo .EQU $91 ; A in, C high
out, C low in, B out. Used by busy-check function.
;8255 Bit Configuration Mode
; Bit set/reset Commands for the E,
RW, RS LCD lines:
; NOTE: With bit 7 being 0 instead of 1, we are in Bit Config Mode
and not Port Config Mode.
; These commands will apply to only Port C:
Command .EQU $0a ; Reset LCD bit #4 portC bit
#5 (RS) 0000 101-0
Data .EQU $0b ; Set LCD bit #4 portC bit #5 (RS)
0000 101-1
Write .EQU $0c
; Reset LCD bit #5 portC bit #6 (RW) 0000 110-0
Read .EQU $0d ; Set LCD bit #5 portC bit #6 (RW)
0000 110-1
Disable .EQU $0e ;
Reset LCD bit #6 portC bit #7 (E) 0000 111-0
Enable .EQU $0f
; Set LCD bit #6 portC bit #7 (E)
0000 111-1
; Define number of Commands and
length of string Data
numComm .EQU $4 ; Number of Commands.
numData .EQU $10 ; Number of
string bytes.
; Initialize RAM and 8255
LD SP, $FFFF
; Set stack pointer to top of RAM.
LD C, CWRadr
LD A, pAoChoCliBo ; Port mode config cmd to 8255:
A out, C high out, C low in, B out.
OUT (C), A
REPEAT: CALL Delay
Assembly Code Overview:
configure LCD
The next chunk of code will be LCD
configuration.
; Config the LCD
LD A, $38
; Function set Command: 8-bit mode, AC=0, 2 lines, 5x7 characters.
initLCD:
LD C, CWRadr
LD D, Command
OUT (C), D
; Set RS low for command (select the instruction register).
LD D, Write
OUT (C), D
; Reset RW pin for writing to LCD.
OUT (pAadr), A ; Place the 38h Command into
portA.
LD D, Enable ;
Start LCD pulse.
OUT (C), D
; ......Enable the LCD.
Call Delay
; ......Slow the pulse.
LD D, Disable ;
......Disable the LCD.
OUT (C), D
; End LCD pulse.
|
Assembly Code Overview: send
commands and data
; This part sends 4 Commands to the LCD
(clear display, set DD RAM address, turn on display with
; cursor hidden, and set entry mode 6):
LD HL, CmndBeginAdr
; Set HL to point the first Command.
LD B, numComm
; Put the number of Commands to be sent in B.
nextComm:
CALL sendCommHL
; Send (HL) as a Command.
INC HL
; Point to the next Command.
DJNZ nextComm
; Loop until all 4 Commands are sent.
; This part sends Data strings to the LCD
LD HL, DataBegAdr ; Set HL to point the
first string byte.
LD B, numData
; Put the number of string Data bytes to be sent in B.
nextData:
CALL sendDataHL
; Send (HL) as string Data.
INC HL
; Point to the next string byte.
DJNZ nextData
; Loop until all string bytes are sent.
;HALT
JP REPEAT
; sendDataA sends the Data in A to the LCD.
; sendDataHL sends the Data in (HL) to the LCD.
; sendCommA sends the Command in A to the LCD.
; sendCommHL sends the Command in (HL) to the
LCD.
sendDataHL:
LD A, (HL) ; Put the Data to be sent to the LCD in
A.
sendDataA:
PUSH BC ; Save BC and DE on Stack.
PUSH DE
LD E, Data
JP Common
sendCommHL:
LD A,(HL)
sendCommA:
PUSH BC ; Save BC & DE on Stack.
PUSH DE
Common:
; Removed BusyCheck.
OUT (C), E
; Set/reset RS according to the content of register E (Command or
Data).
LD D, Write
OUT (C), D
; Reset RW pin (low) for writing to LCD.
OUT (pAadr), A ; Place Data/instruction to be
written into portA.
PUSH HL
; ------------Save HL (HL is also used by Delay).
CALL longDelay ; ------------Delay added between
character reads can create a scroll effect.
POP HL
; ------------Recover HL.
LD D, Enable ; Start LCD
pulse.
OUT (C), D
; ......Enable the LCD.
LD D, Disable ;
......Disable the LCD.
OUT (C), D
; End LCD pulse.
POP D
; Restore DE.
POP BC
; Restore BC.
RET
; Return to CALLer.
; pDelay uses what you put in HL before you called the PDelay
routine.
longDelay:
LD HL, $3F3F
JP pDelay
Delay:
LD HL, $0200 ; Originally
$1010. $0200 is adequate to avoid busy-check function.
; $3F3F = slow scroll.
pDelay:
DEC L
JP NZ, pDelay
DEC H
JP NZ, pDelay
RET
; Return to CALLer.
; 4 Commands and 16-character string
CmndBeginAdr:
.db $01,$80,$0c,$06 ; Clear display, set DD RAM
address, turn on display with cursor hidden,
; and set entry mode
DataBegAdr:
.db $20h,$21,$21,$20,$5a,$65,$64,$38,$30,$2e,$63,$6F,$6D,$20,$21,$21 ; !!
Zed80.com !!
; 0 1 2 3 4 5 6 7 8 9 a b c d e f
.END
|
