Ziatech Corporation ZT 8825, Hardware Manual

Page: 57 / 129

Application Examples
Assembly Language Setup
The following example is written in Assembly language. The
ZT 8825 is loaded with 8 x 32K RAM. The 20-bit memory address
starts at 8000:000 (segment 8000 or 512K).
;MEMORY EQUATES
START_MAP EQU 20H ;=SEGMENT 8000H SHIFTED RIGHT 10 TIMES
SIZE EQU 16 ;16 X 16K = 256K
;8825 I/O ADDRESSES
LO_ADDR EQU 0EE68H
HI_ADDR EQU 0EE69H
DATA EQU 0EE6AH
CONFIG EQU 0EE6BH
;CONFIG REGISTER EQUATES
ALT_REG EQU 80H
VALID EQU 80H ;VALID PAGE
EN_MAP_WR EQU 0EH
EN_BOARD EQU 0BH
MOV DX, CONFIG
MOV AL, EN_MAP_WR
OUT DX, AL ;ENABLE WRITES TO MAP REGISTER
MOV DX, HI_ADDR
MOV AL, 0
OUT DX, AL ;SELECT LOWER 64 MAP REGISTERS
MOV AL, 0 ;START AT REGISTER 0
MOV CX, 64 ;CLEAR ALL 64 MAP REGISTERS
MOV AH, 0 ;NOT VALID PAGE
CLEAR_LOOP:
MOV DX, LO_ADDR
OUT DX, AL ;SELECT NEXT MAP REGISTER
XCHG AH, AL
MOV DX, DATA
OUT DX, AL ;CLEAR IT TO 0
XCHG AH, AL
INC AL
LOOP CLEAR_LOOP
MOV CX, SIZE
MOV AL, START_MAP
MOV AH, VALID
INIT_LOOP:
MOV DX, LO_ADDR
OUT DX, AL ;SELECT WINDOW
MOV DX, DATA
XCHG AH, AL
OUT DX, AL ;ENABLE PAGE
XCHG AH, AL
INC AL ;INCREMENT WINDOW NUMBER
4-2
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