Product specifications

The ascii values of the characters we wish to output will provide the correct pattern
number to be loaded into the text display screen area to extract the correct pattern
shape.
;
;STRING -PRINT A STRING ROUTINE
;
; VDP SHOULD BE IN TEXT MODE ON ETYR
; START ADDRESS OF STRING POINTED TO BY HL
; SCREEN ADDRESS TO WHICH STRING MUST GO IN DE
; STRING MUST BE DELIMITED BY A ‘$’
;
; NO OTHER PARAMETERS REQUIRED
; NO REGISTERS AFFECTED EXCEPT HL WHICH POINTS
; TO ‘$’ CHARACTER ON EXIT
;
MESSAGE: DB ‘This is an ascii string$’
;
START: LD HL,MESSAGE ;Set HL to point to start address of
;text string
LD DE,7144 ;Set DE to point to start address at
;which the text string is to be output
CALL STRING ;Output string to screen
RET ;Return to calling routine
;
STRING: PUSH AF ; Save Acc and flags
PUSH BC ;Save Bc register pair
CALL VSETOT ; Set VDP write to VRAM pointer to start
;address for text output
STRIN1: LD A,(HL) ;Load text byte into Acc
CP ‘$’ ;Test to see whether if character is
;a ‘$’
RET Z ;If true then return to calling routine
;else drop through to line STRIN2
STRIN2: LD C,A ;Load text byte into output register
CALL VDOUTP ;Output text byte to VRAM
INC HL ;Increment text pointer to point to next
;byte in text string
JR STRIN1 ;Go back to STRIN1 and do it again
Graphics 1 Mode
2.6
Graphics 1 mode is the other graphic mode available on the MTX and is not normally
allowed from BASIC. It can be enabled with ease in assembler, and does have
certain useful features. The features it provides are summarised in the table below.
Screen 768 character positions (24 rows by 32 columns) with up to 256
unique characters at any time in an 8 (Horizontal) by 8 (Vertical) pixel
size.