Communicator Module Layout
==========================

Module header
-------------
0x0000-2 BRL <relative entry point> // &82, &nn, &nn
0x0003-5 <size of module>-2 // Offset to CRC word at end of module
0x0006-7 dw 0x0100   // BCD version number, eg 1.00
0x0008   db flags1   // module flags
0x0009   db flags2   // module flags
0x000A   dd 0x00     // module flags
0x000B   db 0x00     // module flags
0x000C-D dw 0x0000   // reserved for expansion of module's own use
0x000E ASCIIZ module name and command table
...    ASCIIZ help strings
...    Module content
zzzzzz Offset at 0x0003-5 points to here
...      dw 0x????   // module CRC
...                  // &FF padding to page boundary 

The text strings are deliminated with '/', eg "MOS/HELP/CLOSE" with | used
to escape the next character, eg "file WR|/wr"

Module flags:
MHCPOS &0001 position-independent code
MHCBNK &0002 bank-independent code
       &0004
MHCODE &0008
       &0010
MHCFS  &0020 filing system interface support
MHCDEV &0040 device driver interface support
MHCBAS &0080 BASIC program
MHCMEN &0100 module may appear in MENU
MHCVPD &0200 VIEW printer driver

MHCONE       Module may appear only one on the main menu
MHCMKL       Module may not be killed once started from the main menu

Service calls appear to be:
XX=sevice number. Must be an even number as used as offset to JMP (addr,X)
On return: SEC: not claimed, registers probably should be preserved
           CLC: claimed, registers may hold values

XX=&007E: start a BASIC program in a module
          On return, CLC, AA=PAGE of program to RUN

If module contains BASIC, scan for:
xxxx db &62
yyyy dw offset
zzzz 
zzzz+offset=>start of BASIC program


... dw CRC // 'length' is offset to this byte
... end of module



Service calls appear to be:
XX=sevice number. Must be an even number as used as offset to JMP (addr,X)
On return: SEC: not claimed, registers probably should be preserved
           CLC: claimed, registers may hold values

XX=&0000: run module
XX=&007E: start a BASIC program in a module
          On return, CLC, AA=PAGE of program to RUN


Entry points in MOS memory
&00FF80
&00FF84
&00FF88
&00FF8C
&00FF90 Called with X=something
&00FF94
&00FF98
&00FF9C
&00FFA0

High memory appears to be opposite way around to low memory
FCxxxx - ROM 3
FDxxxx - ROM 2
FExxxx - ROM 1
FFxxxx - ROM 0 with MOS core

FFxxxx appears to be paged into 00xxxx on RESET

&mmAC00 MOS workspace in bank &mm

Low memory:
&00A5xx - equiv. of BBC &0002xx, vectors and OSBYTE variables
&00A52A/B - INSV
&00A52C/D - REMV
&00A536   - OSBYTE 166
&00A58F   - OSBYTE 255
etc.

&00FFxx   - Entry points to MOS

High memory:
&45xxxx - Electron memory map
&450000 - screen memory
&458000 - keyboard
&45FE00 - ULA