Debugging
The KIM-1 monitor has several debugging features that require to fill the interrupt vectors at 17FA, and 17FE. Enter 1C00 here.
17FA NMIT for Single stepping
17FE IRQV for BRK handling

You can single step your program, examining and altering memory and registers before the next instruction is executed.
Or place breakpoints in your program at interesting points. And use a combination of both.

The debugging uses these zeropage locations. Stored by SAVE ($1C00) and loaded by G or GO via GOEXEC.

0069   00EF                        .ORG $00EF      
0070   00EF             ;       	MPU REG.  SAVX AREA IN PAGE 0   
0071   00EF             ;
0072   00EF             PCL     .BLOCK  1          ; PROGRAM CNT LOW
0073   00F0             PCH     .BLOCK  1          ; PROGRAM CNT HI
0074   00F1             PREG    .BLOCK  1          ; CURRENT STATUS REG.
0075   00F2             SPUSER  .BLOCK  1          ; CURRENT STACK POINT
0076   00F3             ACC     .BLOCK  1          ; ACCUMULATOR
0077   00F4             YREG    .BLOCK  1          ; Y INDEX
0078   00F5             XREG    .BLOCK  1          ; X INDEX

The SST slide switch activates single step activation
After a G one instruction is executed and the monitor is active again
Now you can inspect/change memory and the saved registers in zeropage, and continue after the last executed instruction.

Using a BRK as breakpoint, temporary replacing the instruction at this location manually.
A BRK instruction lets the CPU execute the IRQ vector. When this is 1C00, SAVE routine is executed, saving all registers in EF and on.

Example of a BRK breakpoint

KIM
00F8 00 200
0200 00 A9.  LDA #$55
0201 00 55.
0202 00 A2.  LDX #$44
0203 00 44.
0204 00 00.  BRK
0205 00 0200
0200 A9 G
KIM
0206 00 EF
00EF 06
00F0 02
00F1 30
00F2 00
00F3 55
00F4 00
00F5 44

As you can see, the BRK at 0205 has made the CPU jump to SAVE:
– EF has the Program counter 0206 (the first location after the BRK)
F3 has A, 55
F5 has X, 44
Now you can replace the BRK at 0205 with what was originally there and continue at 0205. Or start with Single Stepping by sliding SST swicth to ON.