Technical data

MC68HC912B32 MOTOROLA
MC68HC912B32TS/D 119
The CPU must be in background mode to execute commands that are implemented in the BDM ROM.
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. These commands are shown in Table 44.
NOTES:
1. STATUS command is a specific case of the READ_BD_BYTE command.
2. ENABLE_FIRMWARE and ENTER_TAG_MODE are specific cases of the WRITE_BD_BYTE command.
Table 43 BDM Commands Implemented in Hardware
Command Opcode (Hex) Data Description
BACKGROUND 90 None Enter background mode (if firmware enabled).
READ_BD_BYTE E4
16-bit address
16-bit data out
Read from 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.
STATUS
1
E4
FF01,
0000 0000 (out)
READ_BD_BYTE $FF01. Running user code (BGND in-
struction is not allowed).
FF01,
1000 0000 (out)
READ_BD_BYTE $FF01. BGND instruction is allowed.
FF01,
1100 0000 (out)
READ_BD_BYTE $FF01. Background mode active (wait-
ing for single wire serial command).
READ_BD_WORD EC
16-bit address
16-bit data out
Read from memory with BDM in map (may steal cycles if
external access) must be aligned access.
READ_BYTE E0
16-bit address
16-bit data out
Read from 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.
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 ex-
ternal 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 execu-
tion 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 ex-
ternal 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.