Development Support
MC68HC812A4 Data Sheet, Rev. 7
216
Freescale Semiconductor
READ_WORD
E8
16-bit address
16-bit data out
Read from memory with BDM out of map (may steal cycles
if external access); must be aligned access
WRITE_BD_BYTE
C4
16-bit address
16-bit data in
Write to memory with BDM in map (may steal cycles if
external access); data for odd address on low byte, data for
even address on high byte
ENABLE_ FIRMWARE(2)
C4
FF01,
1xxx xxxx (in)
Write byte $FF01, set the ENBDM bit. This allows
execution of commands which are implemented in
firmware. Typically, read STATUS, OR in the MSB, write the
result back to STATUS.
WRITE_BD_WORD
CC
16-bit address
16-bit data in
Write to memory with BDM in map (may steal cycles if
external access); must be aligned access
WRITE_BYTE
C0
16-bit address
16-bit data in
Write to memory with BDM out of map (may steal cycles if
external access); data for odd address on low byte, data for
even address on high byte
WRITE_WORD
C8
16-bit address
16-bit data in
Write to memory with BDM out of map (may steal cycles if
external access); must be aligned access
1. STATUS command is a specific case of the READ_BD_BYTE command.
2. ENABLE_FIRMWARE is a specific case of the WRITE_BD_BYTE command.
Table 17-3. BDM Firmware Commands
Command
Opcode (Hex)
Data
Description
READ_NEXT
62
16-bit data out
X = X + 2; read next word pointed to by X
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
X = X + 2; write next word 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 BDM
TAGGO
18
None
Enable tagging and go to user program
Table 17-2. BDM Commands Implemented in Hardware (Continued)
Command
Opcode (Hex)
Data
Description