Section 2 - Commodore Computers

May. May, 1982, Issue 24 2.::1 COMPUTE! COMPUTEI 133
contents of the A, X, Y, Sand P registers, and most
importantly, perform pelf arm the instruction, so that
branches are followed properl y and new code is
branches are followed properly and new code is
created.
.
A certain amount of discretion is involved with
A certain amount of discretion is involved with
these. Trace scrolls the information up the CRT
about twice as fast t as a BASIC LIST. To see what
it's doing in detail really y requires a printer, and
even then it's very easy to go through a ream of
paper needlessly if trace encounters loops of any
length. I'd be inclined to say the best use of trace
would be in debugging your own programs on
CRT only, to the extent of insuring that there are
no infinite nite loops, and that the final al RTS is correct.
Step has much more potential, the pace is user­
Step has much more potential, the pace is usercontrolled.
If trapped in a long loop, one can simply
step out by keying a step to the alternate branch.
step out by keying a step to the alternate branch.
Better yet, rather than stepping out explicitly,
monitor in the information that will cause the
desired branch and then step the location again.
ThisT will ensure that subsequent step-traces will be
getting correct code.
A cautionary note: since trace and step do
perform rm the instructions, the same caution has to
be observed as with any POKE or user-written
machine code routine. Switches will be set or reset,
no permanent damage can be done, but the system
can be crashed or DOS can n be disabled.
10 REM MAKE SOFTMON SoFTMoN
20 D$ 0$ ■= CHR$ (13) ( + CHR* CHR$ (4)
)
30 DEF FN LB(D> LB (0) D0 - 256 * INT (D (0 / 256)
)
40 DEF FN HB(D) HB (0 ) INT (D (0 / 256)
)
50 DEF FN DC (I) = PEEK (I) (Il + 256 * PEEK (I( I + 1)
60 REM PAGE ADDRESSES IN *4B00-4FFF $4800-4FFF BY HEX X DIBIT DIGIT
70 S8 = 18432:S9 = 18688:SA = 18944:SB = 19200:SC =
19968:SF : SF = 20224:SG = 20480
70 S8 = 18432:S9 = 18688:SA ■ 18944:SB ■ 19200:SC = 19456:SD = 19712:SE =
80 REM A1,A2,A4 Al,A2 , A4 HIGH 8c & LOW BYTES
90 LI Ll = 60:HI 60:Hl = 6i:L2 61 :L2 = 62:H2 = 63:L4 = 66:H4 : H4 = 67
100 MS = 63488:ME : = 65535
110 PRINT "COPYING MONITOR INTO $4800-$4FFF"
110 PRINT "COPYING MONITOR INTO *4800-*4FFF"
120 POKE LI, Ll, FN LB(MS): ) : POKE HI, Hl, FN HB(MS): ) : POKE UL2, FN LB(ME): ) : POKE H2,
FN HB(ME): ) : POKE L4, FN LB(S8): LB (S8 ) : POKE H4, FN HB(S8) HB (S8 )
130 CALL 65068
140 PRINT "CHANGING ADDRESSES FOR JSR'S 'S AND JMP'S" 'S"
150 PRINT "CHANGED ADDRESSES ARE LISTED"
150 PRINT "CHANGED ADDRESSES ARE LISTED"
160 FOR I = S8 TO SG - 1: 1:P P = PEEK (Il: (I): IF P < > 32 AND P < > 76 THEN
190
170 P = PEEK (I (1+2): + : IF P < 248 THEN 190
180 POKE I + 2, P - 176: PRINT I
180 POKE I + 2,P - 176: PRINT I
190 NEXTNE XT
230 PRINT "READING NEW DATA AND POKING"
240 FOR I = SA + 64 TO SA + 214: READ P: POKE I I,P: , NEXT
XT
19456:SD = 19712:SE =
200 PRINT "MAKING A FEW OTHER ADDRESS CHANGES"
210 POKE SA + 235,74: POKE SE + 168,77: : POKE SF + 127,79: POKE SF + 191,
78: POKE SF + 195,79: POKE SF + 207,237
220 POKE SF + 210,236: 236: POKE SF + 233,195: POKE SF + 253,79: POKE SF + 25
5, 5,74: 74: POKE SF + 106,163
230 PR I NT "READ I NG NEill DATA AND PoK I NG"
250 FOR I = SA + 253 TO SB + 29: READ P: POKE I , P: NEXT
250 FOR I
SA + 253 TO SB + 9: READ P: POKE I,P: NEXT
260 FOR I = SE + 194 TO SE + 201: READ P: Pi POKE I I,P: NEXT
270 PRINT "NEWMON IS NOW READY": : PRINT: : PRINT "TO ENTER IT, CALL 20329"
: PRINT "OF:" "OR"
280 !80 PRINT "ENTER MONITOR WITH CALL -151": PRINT "AND THEN KEY ''4F69S'"
4F69G ' "
290 !90 INPUT "SAVE SoFTMON SOFTMON ? ";Q$: IF Q$ > = "Y" THEN PRINT "SAVING SoFTM
SOFTM
ON,A$4800,L$800": 0N,A*4B00,L$800": PRINT D$"BSAVE SoFTMoN,A$4800,L$800"
SOFTMON,A$4800,L*BOOl
300 END
310 DATA 255,255,255, 5,2! 32, >2,208,72,104,133,44,104,133,45,162,8,189,16
208,72, 16