M68HC12A4EVB Freescale Semiconductor, M68HC12A4EVB Datasheet - Page 294

• Manufacturer Part Number: M68HC12A4EVB
• Manufacturer: Freescale Semiconductor

Specifications of M68HC12A4EVB

• Lead Free Status / Rohs Status: Not Compliant

Development Support
The second type of BDM commands are called firmware commands because they are implemented in a
small ROM within the HC12 MCU. The CPU must be in background mode to execute firmware
commands. The usual way to get to background mode is by the hardware command BACKGROUND. The
BDM ROM is located at $FF20 to $FFFF while BDM is active. There are also seven bytes of BDM
registers which are located at $FF00 to $FF06 while BDM is active. The CPU executes code from this
ROM to perform the requested operation. The BDM firmware watches for serial commands and executes
them as they are received. The firmware commands are shown in
Each of the hardware and firmware BDM commands starts with an 8-bit command code (opcode).
Depending upon the commands, a 16-bit address and/or a 16-bit data word is required as indicated in the
tables by the command. All the read commands output 16 bits of data despite the byte/word implication
in the command name.
294
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.
WRITE_BD_WORD
WRITE_WORD
WRITE_BYTE
Command
WRITE_NEXT
READ_NEXT
WRITE_PC
WRITE_SP
Command
READ_PC
READ_SP
WRITE_D
WRITE_X
WRITE_Y
READ_D
READ_X
READ_Y
TRACE1
TAGGO
GO
Opcode (Hex)
Table 18-2. BDM Hardware Commands (Continued)
CC
C0
C8
Opcode (Hex)
Table 18-3. BDM Firmware Commands
M68HC12B Family Data Sheet, Rev. 9.1
62
63
64
65
66
67
42
43
44
45
46
47
08
10
18
16-bit address
16-bit address
16-bit address
16-bit data in
16-bit data in
16-bit data in
Data
16-bit data out
16-bit data out
16-bit data out
16-bit data out
16-bit data out
16-bit data out
16-bit data in
16-bit data in
16-bit data in
16-bit data in
16-bit data in
16-bit data in
None
None
None
Data
Write to memory with BDM in map (may steal cycles if external
access) must be aligned access.
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 to memory with BDM out of map (may steal cycles if
external access) must be aligned access.
X = X + 2; Read next word
pointed to by X
Read program counter
Read D accumulator
Read X index register
Read Y index register
Read stack pointer
X = X + 2; Write next word
pointed to by X
Write program counter
Write D accumulator
Write X index register
Write Y index register
Write stack pointer
Go to user program
Execute one user instruction
then return to BDM
Enable tagging and go to
user program
Table
Description
Description
18-3.
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