Technical data

172Bug Implementation
http://www.mcg.mot.com/literature 3-3
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If you have used one or more of Motorola’s other debugging packages, you
will find the CISC 172Bug very similar. Some effort has also been made
to make the interactive commands more consistent. For example,
delimiters between commands and arguments may be commas or spaces
interchangeably.
172Bug Implementation
MVME172Bug is written largely in the "C" programming language,
providing benefits of portability and maintainability. Where necessary,
assembler has been used in the form of separately compiled modules
containing only assembler code. No mixed language modules are used.
Physically, 172Bug is contained in a single 27C040 DIP EPROM installed
in socket XU2, providing 512KB (128K longwords) of storage.
Optionally, the 172Bug can be loaded and executed in a single Flash
memory chip. The executable code is checksummed at every power-on or
reset firmware entry, and the result (which includes a pre-calculated
checksum contained in the memory devices) is verified against the
expected checksum.
Memory Requirements
The program portion of 172Bug is approximately 512KB of code,
consisting of download, debugger, and diagnostic packages and contained
entirely in Flash memory or PROM.
The 172Bug executes from address $FF800000 whether in Flash or
EPROM. If you remove the jumper at J21 pins 9 and 10, the address spaces
of the Flash and EPROM are swapped. For MVME172-2xx series boards
(MVME172LX), the factory ship configuration is with jumper J21 pins 9-
10 removed (172Bug operating out of EPROM).
The 172Bug initial stack completely changes 8KB of SRAM memory at
address offset $C000 from the SRAM base address, at power-up or reset.