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X16 Reference - 07 - Machine Language Monitor.md

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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