Product specifications

8. Now add the value obtained by subtracting the original value of VAZERO
(which you noted down), from the original value of NBTOP, BASTOP and
BASTBO.
9. Set VAZERO to its original value
10. Exit panel and return to BASIC
11. Save the appended code
At this point you will have an appended section of code saved on tape.
Screen Output using RST 10
3.5
The ROM calls for screen output are all in the form of restart 10 calls. Following each
of these calls is data which tells the ROM routine what to do. At first this is a little
confusing as data is stored in the path of the program, but is in fact remarkable easy
to use.
Writing ASCII characters to the Screen
The following RST 10 routine passes the ascii representations of registers B and C to
the screen.
START: LD BC.”TM”
RST 10
DB 192
RET
A less trivial example would be the following:
START: LD, E,8
LD HL, DATA
LOOP: LD A,(HL)
LD B,0
LD C,A
RST 10
DB 192; write BC token
DEC E
JR NZ, LOOP
RET
DATA: DB “MEMOTECH”
Try changing the line that loads B with zero to load B with the space character and
see what happens.
Sending Messages to the Screen
To avoid the complication of the above routine we can send a complete string in the
following way:
RST 10
DB £8D, “MEMOTECH LTD”
RET