Product specifications

;
; INISCR INITIALISE PATTERN NAME TABLE (DISPLAY SCREEN)
;
; NO PARAMETERS REQUIRED ON ENTRY
; NO REGISTERS AFFECTED ON EXIT
;
INISCR: PUSH AF ;Save Acc and flags
PUSH BC ;Save BC register pair
PUSH DE ;Save DE register pair
PUSH HL ;Save HL register pair
LD HL,768 ;Set up loop counter to equal
;768 – This is the size of the
;display screen
LD C,0 ;Set byte to be output to each
;sequential screen position to zero
LD DE,15360 ;Load DE with start address of screen
CALL VSETOT ;Set VDP write to VRAM pointer
;to point to start of screen
;
INISC1: CALL VDOUTP ;Output display byte to screen
INC C ;Increment display byte
DEC HL ;Decrement loop counter
;
LD A,H ;If loop counter < > 0 then
OR L ;goto INISC1 else drop through
JR N,INISC1 ;to INISC2
;
INISC2: POP HL ;Get old HL register pair
POP DE :Get old DE register pair
POP BC ;Get old BC register pair
POP AF ;Get old Acc and flags
RET ;Return to calling routine
Text Mode
2.5
Text mode is either decimal or hex, alphanumeric, or the low byte of a label.
eg: - <label>: DB <dec/hex No.> and/or “<string>” and/or <label>
NB: Using a label will generator an out of range error but ignoring this error leaves the
low byte of the label 8 (Vertical) pixel size.
The character patterns can be dynamically changed to give any number of character
patterns limited by the amount of storage space in Z80 RAM for the extra pattern
libraries.
The display colours can be any one of 15 including transparent for the backdrop
colour, and any one of 15 including transparent for the text colour.