IBM 6400 series Maintenance Manual page 155

Debug SIMM — The debug SIMM contains fast static RAM that
automatically replaces the flash memory. Boot code checks for the debug
SIMM and, if found, copies the contents of flash memory into the SIMM,
then remaps the address of the SIMM to the location of flash. This allows
breakpoints and single-stepping from the MTOS debugger. When the
debug SIMM is found, boot code displays "DEBUG SIMM ACTIVATED"
on the panel and out the debug port.
Verify DC Program — Boot code calculates a checksum at every power
up to verify that the program has not been corrupted. If the checksum
does not match, boot code displays "ERROR: DC PROGRAM NOT
VALID".
Check Security — The security check verifies that security PAL supports
the software that is loaded in flash memory. If the PAL does not support
the software, boot code displays "SECURITY CODE VIOLATION".
Check Required DRAM — Boot code checks whether the amount of
DRAM required to run the DC program is larger than the amount of
DRAM in the printer. If so, it displays the message "ERROR: PROGRAM
NEEDS MORE DRAM".
Tell EC Processor to Finish Booting — Boot code informs the EC
processor that everything is okay and can finish booting up.
Diagnostics Passed — If all tests pass, boot code displays
"P05 DIAGNOSTIC TEST PASSED". At this point, the ribbon motors
engage. Boot code then jumps to the start address of the DC software.
Display DC Program Information — Boot code sends the following
information out the debug port: the compile time, date, and the address it
will jump to to start the DC program.
Waiting Ethernet — If boot code earlier detected an Ethernet adapter, it
places the message "WAITING FOR THE ETHERNET ADAPTER" on
the LCD so the user will not think the printer has crashed.
Jump Back into Flash and Clear DRAM — Boot code jumps back into
flash memory, then clears the DRAM that held the boot code.
Jump to MTOS — Jump to start initialization of the MTOS (Multi-Tasking
Operating System).
Troubleshooting 155