Chapter 6 Background Debug Module (BDMV4) Block Description
Freescale Semiconductor
MC9S12C-Family / MC9S12GC-Family
177
Rev 01.24
firmware. The standard BDM firmware watches for serial commands and executes them as they are
received.
The firmware commands are shown in
.
6.4.5
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.
NOTE
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 6-6. 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
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. If enabled, ACK will occur when leaving active
background mode.
GO_UNTIL
(2)
2. Both WAIT (with clocks to the S12 CPU core disabled) and STOP disable the ACK function. The GO_UNTIL command will not
get an Acknowledge if one of these two CPU instructions occurs before the “UNTIL” instruction. This can be a problem for any
instruction that uses ACK, but GO_UNTIL is a lot more difficult for the development tool to time-out.
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
18
None
Enable tagging and go to user program. There is no ACK pulse related to
this command.
Summary of Contents for MC9S12C Family
Page 689: ......