mc68hc912b32fu8 Freescale Semiconductor, Inc, mc68hc912b32fu8 Datasheet - Page 120

• Manufacturer Part Number: mc68hc912b32fu8
• Description: 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

16.2.4 BDM Registers
INSTRUCTION — BDM Instruction Register (hardware command bit explanation)
H/F — Hardware/Firmware Flag
DATA — Data Flag
R/W — Read/Write Flag
BKGND — Hardware request to enter active background mode
120
MOTOROLA
Seven BDM registers are mapped into the standard 64-Kbyte address space when BDM is active. The
registers can be accessed with the hardware READ_BD and WRITE_BD commands, but must not be
written during BDM operation. Most users will only be interested in the STATUS register at $FF01; other
registers are only for use by BDM firmware and logic.
The instruction register is discussed for two conditions: when a hardware command is executed and
when a firmware command is executed.
The bits in the BDM instruction register have the following meanings when a hardware command is
executed.
WRITE_NEXT
READ_NEXT
0 = Firmware instruction
1 = Hardware instruction
0 = No data
1 = Data included in command
0 = Write
1 = Read
0 = Not a hardware background command
1 = Hardware background command (INSTRUCTION = $90)
WRITE_PC
WRITE_SP
Command
READ_PC
READ_SP
WRITE_D
WRITE_X
WRITE_Y
READ_D
READ_X
READ_Y
TRACE1
TAGGO
GO
Bit 7
H/F
DATA
Opcode (Hex)
6
62
63
64
65
66
67
42
43
44
45
46
47
08
10
18
Table 44 BDM Firmware Commands
R/W
5
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
BKGND
None
None
None
Data
4
W/B
Go to user program
Execute one user instruction then return to BDM
Enable tagging and go to user program
3
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
BD/U
2
Description
1
0
MC68HC912B32TS/D
Bit 0
MC68HC912B32
0
(BDM) $FF00