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$R
$FF DC FC 6EFD 0100 A042 REGISTER DUMP BEFORE RUNNING PROGRAM
$G
$R
$FF DC FC 6EFD 0100 A042 NOTE R DUMP THE SAME AFTER RUNNING
$J 0100
$R
$FF DC FC 6EFD 0100 A042 THE SAME AFTER A JUMP
$M 010A AT THIS POINT THE JUMP TO SWTBUG CONTROL
$010A 7E 3F IS REPLACED BY A SWI. NOTE THE VALUE
$010B 50 OF THE REGISTERS AFTER THE NEXT DUMP.
$G
$F9 FF 00 1234 010A 0FF9 REGISTER DUMP GIVEN BY SWI
$R
$F9 FF 00 1234 010A 0FF9 DUMP SHOWS PROGRAM CHANGES
$
$FF DC FC 6EFD 0100 A042 R DUMP AFTER RESET
In the above program you will notice that the register dump after running the program is the
same as before even though the program contained statements that changed the processor’s
registers. The register dump did not reflect these changes because the new conditions were not
pushed on the computer’s stack. Note, however, the register dump did reflect the change when
the last instruction was a software interrupt -- a SWI instruction will push the processor’s status
on the stack and then display the contents of the registers.
CT-1024 CLEAR SCREEN COMMAND C
The C command outputs a home-up (10
16
) and an erase to end of frame (16
16
) control
characters for the clearing of the screen on a SWTPC CT-1024 or equivalent terminal system.
GO TO USER’S PROGRAM FUNCTION G
Upon entering a G command, SWTBUG® will transfer control to the user’s program by
executing a RTI (return from interrupt) instruction. This effectively causes the computer to jump to
the memory address stored in memory locations A048 and A049 in the SWTBUG® RAM. A048
contains the most significant byte and A049 the least significant byte of the memory address. If,
for example, you wish to execute a program starting at 0100, change A048 to a 01 using the M
function and change A049 to 00. Typing a G will then cause the computer to execute the program
whose starting address is 0100. Upon entering a program using the G function, the stack pointer
will be set at A049. The G function is also used to restart a program after a breakpoint has been
moved. In this case A048 and A049 should not be changed. See the Breakpoint section for
further information.
JUMP TO USER’S PROGRAM J(addr)
The J command will cause the computer to execute the program whose starting address is
given in the entered address. The J command does not look at locations A048 and A049. The
stack pointer will be set at A042 upon entering a program with a jump command. Example: J
0100. If a non-hex character is entered, SWTBUG® control will resume.
ASCII TAPE PUNCH COMMAND P
The P command provides a means for storing the contents of specified memory on either
cassette or paper tape. Normal output from the computer during a punch is thru either an MP-C
or MP-S serial interface on I/O port 1, but a MP-C interface on I/O 0 can be selected. (See the
description of the O command.) To use the P command, the upper and lower limits of the range
to be punched must first be stored in locations A002-A005 of the SWTBUG® RAM. If you wanted
to punch from addresses 0123 to 4567 (inclusive) you would use the memory examine and
change functions to set computer memory as follows.