7. PROCEDURES FOR PROCESSING PROGRAMS
7.1. Removing the block program
Length: 42
Number of variables: 2
Checksum: 5977
Purpose: This program removes the block BASIC-programs, which
lies between the lines defined by the user.
Variables:
Name: start line no
Length: 2
Cell: 23296
Comment: The number of first
lines to be removed.
Name: end line no
Length: 2
Cell: 23298
Comment: The last line number to be removed.
Calling the program:
RANDOMIZE USR address
Error control: if they have
The following errors, then the procedure stops without deleting
rows BASIC-programs:
- If the last line number
less than the first line number;
- If between the two strings have a program in BASIC;
- If one line numbers
or both are 0.
Comment: This program is rather slow to remove
a large block of software
lines, but, nevertheless, to work with it still more convenient
than deleting rows manually.
Do not enter a line number greater than 9999.
LISTING machine code
Assembly label number to VVODA147.
LD HL, (23296) 42 0 91
LD DE, (23298) 237 91 February 1991
LD A, H 124
OR L 181
RET Z 200
LD A, D 122
OR E 179
RET Z 200
PUSH DE 213
CALL 6510 205 110 1925
EX (SP), HL 227
INC HL 35
CALL 6510 205 110 1925
POP DE 209
AND A 167
SBC HL, DE 237 82
RET Z 200
RET C 216
EX DE, HL 235
NXT_CH: LD A, D 122
OR E 179
RET Z 200
PUSH DE 213
PUSH HL 229
CALL 4120 205 24 16
POP HL 225
POP DE 209
DEC DE 1927
JR NXT_CH 24243
2
How it works:
In a pair of registers HL and DE are loaded starting and
ending row numbers, respectively. These
values are checked and, if one or both of them equal to 0,
the program returns to BASIC.
It then calls the subroutine
ROM at 6510 - it returns the address in memory,
with which to begin the first
line. The same routine is then called again to determine the
address character, standing ENTER after the final string.
In a couple of registers placed HL difference between these
two addresses, and If this value is 0 or
negative, the program returns to BASIC.
The contents of register pair HL
copied to the DE for use DE as a counter. If
count is 0, then the work procedure is completed, and if not,
a routine is called ROM
located at 4120,
which deletes a single character.
After that - back to NXT_CH.
