Datasheet

Background Debug Module
MC9S12DP256 — Revision 1.1
Background Debug Module (BDM)
instruction execution is suspended while the CPU executes the firmware
located in the standard BDM firmware lookup table. The hardware
command BACKGROUND is the usual way to activate BDM.
As the system enters active BDM, the standard BDM firmware lookup
table and BDM registers become visible in the on-chip memory map at
$FF00-$FFFF, and the CPU begins executing the standard BDM
firmware. The standard BDM firmware watches for serial commands and
executes them as they are received. The firmware commands are
shown in Table 122.
Table 122 Firmware Commands
Command
Opcode
(hex)
Data Description
READ_NEXT 62 16-bit data out Increment X by 2 (X = X + 2), then read word X points to.
READ_PC 63 16-bit data out Read program counter.
READ_D 64 16-bit data out Read D accumulator.
READ_X 65 16-bit data out Read X index register.
READ_Y 66 16-bit data out Read Y index register.
READ_SP 67 16-bit data out Read stack pointer.
WRITE_NEXT 42 16-bit data in
Increment X by 2 (X=X+2), then write word to location
pointed to by X.
WRITE_PC 43 16-bit data in Write program counter.
WRITE_D 44 16-bit data in Write D accumulator.
WRITE_X 45 16-bit data in Write X index register.
WRITE_Y 46 16-bit data in Write Y index register.
WRITE_SP 47 16-bit data in Write stack pointer.
GO 08 none Go to user program.
TRACE1 10 none Execute one user instruction then return to active BDM.
TAGGO 18 none Enable tagging and go to user program.
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