Radio Shack TRS-80 Operation Manual page 109

Computer Graphics Operation Manual
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Print graphics screen to graphics printer
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~l~
~ll
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GPRINT
PSECT
GPRINT PUSH
PUSH
PUSH
PUSH
CALL
OR
OUT
CALL
XOR
OUT
LD
LD
LD
LD
LD
CALL
.
,
LOOPI LD
LD
LD
DEC
OUT
COLUMN LD
IN
AND
CALL
LD
PUSH
LD
INC
DECJ DEC
JR
RLC
JR
PAST POP
OR
LD
INC
DJNZ
LD
INC
CP
CALL
~F~~~H
HL
DE
BC
IX
INITG
~DBH
(STATUS) ,A
INITBF
A
(X) ,A
(BPOS) ,A
i
(XLOC) ,A
i
HL,BGMODE
B,l
C,~DH
PRLINE
IX,BUFFER
B,24~
A,B
A
(Y) ,A
HL,MASK
A, (GRAPH)
(HL)
PO,SET~
HL,BPOS
BC
B,
(HL)
B
B
Z,PAST
A
DECJ
BC
(IX)
(IX) ,A
IX
COLUMN
A,7
(HL)
(HL)
Z,PRNDRS
i
iSave registers
iOutput a Control byte to cause
i
y to automatically dec. on a read
iSet A to
~
iInitialize the X position
" " b i t position
" " " location counter
iBegin graphics print mode
ipoint IX at the printer buffer
igo through a whole column of bytes
iPut value in A and decrement
i
so it can be put out as
i
the Y position
ipoint HL at the mask byte
iinput a graphics byte
ichop off all but proper bit
iif result is odd parity set bit
~
i
otherwise bit A is
~
ipoint HL at the bit position
isave register B (for DJNZ loop)
iget count
iincrement (in case it is
~)
imove bit left BPOS number of times
iif done, move on ...
imove bit left one position
irepeat loop
iget loop counter back
imerge A with byte of printer buffer
iput merged result in buffer
iincrement buffer pointer
icontinue loop
iSee
if BPOS has gotten to 8.
i
If it has (printer uses 7 bits)
print the buffer and reset
BPOS to
~
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