Chapter 7: Machine Language Monitor

The built-in machine language monitor can be started with the MON BASIC command. It is based on the monitor of the Final Cartridge III and supports most of its features.

If you invoke the monitor by mistake, you can exit with by typing X, followed by the RETURN key.

Some features specific to this monitor are:

  • The I command prints a PETSCII/ISO-encoded memory dump.

  • The EC command prints a binary memory dump. This is also useful for character sets.

  • Scrolling the screen with the cursor keys or F3/F5 will continue memory dumps and disassemblies, and even disassemble backwards.

The following commands are used to dump memory contents in various formats:

Dump

Prefix

description

M

:

8 hex bytes

I

'

32 PETSCII/ISO characters

EC

[

1 binary byte (character data)

ES

]

3 binary bytes (sprite data)

D

,

disassemble

R

;

registers

Except for R, these commands take a start address and an optional end address (inclusive). The dumps are prefixed with one of the “Prefix” characters in the table above, so they can be edited by navigating the cursor over a printed line, changing the data and pressing RETURN.

Note that editing a disassembled line (prefix ,) only allows changing the 1-3 opcode bytes. To edit the assembly, change the prefix to A (see below).

These are the remaining commands:

Command

Syntax

Description

F

start end byte

fill

H

start end byte [byte…]

hunt

C

start end start

compare

T

start end start

transfer

A

address instruction

assemble

G

[address]

run code

J

[address]

run subroutine

$

value

convert hex to decimal

#

value

convert decimal to hex

X

exit monitor

O

bank

set ROM bank

K

bank

set RAM/VRAM bank/I2C

L

[”filename”[,dev[,start]]]

load file

S

“filename”,dev,start,end

save file

@

command

send drive command

  • All addresses have to be 4 digits.

  • All bytes have to be 2 digits (including device numbers).

  • The end address of S is exclusive.

  • The bank argument for K is

    • 00-FF: switch to main RAM, set RAM bank

    • V0-V1: switch to Video RAM, set VRAM bank

    • I: switch to the I2C address space

  • The bank argument for O is

    • 00-FF: set ROM bank

  • @ takes:

    • 8, 9 to change the default drive (also for L)

    • $ to display the disk directory

    • anything else as a disk command

Monitor Display

MON
C*
   PC  RA RO AC XR YR SP NV#BDIZC
.;E3bb 01 04 00 00 00 F6 ........
.

Column

Description

PC

Program Counter and the current address

RA

Active RAM Bank

RO

Active ROM Bank

AC

Accumulator Value

XR

X Register Value

YR

Y Register Value

SP

Stack Pointer

NV#BDIZC

Status Register

Status Register Bits

Bit Description

N

Negative

V

Overflow Vector

#

Unused

B

A Break Point is Active

D

Decimal Mode Active (also known as Binary Code Decimal)

I

IRQ is Inhibited

Z

Zero Bit

C

Carry Bit