Background Debug Module (S12XBDMV2)
MC9S12XHY-Family Reference Manual Rev. 1.01
Freescale Semiconductor
209
5.4.5
BDM Command Structure
Hardware and firmware BDM commands start with an 8-bit opcode followed by a 16-bit address and/or a
16-bit data word depending on the command. All the read commands return 16 bits of data despite the byte
or word implication in the command name.
8-bit reads return 16-bits of data, of which, only one byte will contain valid
data. If reading an even address, the valid data will appear in the MSB. If
reading an odd address, the valid data will appear in the LSB.
Table 5-7. Firmware Commands
Command
1
1
If enabled, ACK will occur when data is ready for transmission for all BDM READ commands and will occur after the write is
complete for all BDM WRITE commands.
Opcode
(hex)
Data
Description
READ_NEXT
2
2
When the firmware command READ_NEXT or WRITE_NEXT is used to access the BDM address space the BDM resources
are accessed rather than user code. Writing BDM firmware is not possible.
62
16-bit data out Increment X index register 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.
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42
16-bit data in
Increment X index register 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. If enabled, ACK will occur when leaving active
background mode.
GO_UNTIL
3
3
System stop disables the ACK function and ignored commands will not have an ACK-pulse (e.g., CPU in stop or wait mode).
The GO_UNTIL command will not get an Acknowledge if CPU executes the wait or stop instruction before the “UNTIL”
condition (BDM active again) is reached (see
Section 5.4.7, “Serial Interface Hardware Handshake Protocol”
last Note).
0C
none
Go to user program. If enabled, ACK will occur upon returning to active
background mode.
TRACE1
10
none
Execute one user instruction then return to active BDM. If enabled,
ACK will occur upon returning to active background mode.
TAGGO -> GO
18
none
(Previous enable tagging and go to user program.)
This command will be deprecated and should not be used anymore.
Opcode will be executed as a GO command.
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