Product specifications

AND 127 ;SET 'WRITE TO VRAM MODE'
OUT (2),A ;OUTPUT HIGH BYTE ADDRESS
POP AF ;GET OLD ACC
RET
;
;VSETRD - SET UP VRAM ADDRESS POINTER FOR DATA INPUT DEPENDENT
ON ADDRESS HELD IN DE ON ENTRY
;
VSETRD: PUSH AF ;SAVE ACC
LD A, E
OUT (2),A ;OUTPUT LOW BYTE ADDRESS
LD A, D
AND 63 ;SET 'READ FROM VRAM MODE'
OUT (2),A ;OUTPUT HIGH BYTE ADDRESS
POP AF ;GET OLD ACC
RET
;
;VD0UTP-OUTPUT DATA BYTE HELD IN C TO ADDRESS POINTED TO BY AUTO-
INCREMENTING REGISTER ON-BOARD THE VDP
;
VDOUTP: PUSH AF ;SAVE ACC
LD A, C
OUT (1),A ;OUTPUT DATA BYTE
POP AF ;GET OLD ACC
RET
;
;VDINPUT-INPUT A DATA BYTE AND RETURN VALUE IN C FROM ADDRESS
POINTED TO BY THE AUTO INCREMENTING REGISTER ON BOARD
THE VDP
VDINPT: PUSH AF ;SAVE ACC
IN A,(1) ;READ DATA BYTE
LD C,A ;PLACE BYTE IN C'
POP AF ;GET OLD ACC
RET
Using the MTX assembler.
1.7
The MTX assembler is a simple to use in line, assembler called from BASIC. Only the
machine executable OBJECT code is stored in memory, readable assembler
SOURCE code is generated by disassembling the object code and inserting the
relevant text and labels, stored in tables below the object code.
The actual location of the code can change as it is stored as a BASIC fine, within
BASIC. So as a program is extended and edited the location of the code changes.
Writing in Assembler.
As assembler code is stored in a BASIC line it is first necessary to tell the computer at
which BASIC line you wish the code to appear. This is done with the immediate
command ASSEM, eg :