Technical data

MC68HC912B32 MOTOROLA
MC68HC912B32TS/D 121
W/B — Word/Byte Transfer Flag
0 = Byte transfer
1 = Word transfer
BD/U — BDM Map/User Map Flag
Indicates whether BDM registers and ROM are mapped to addresses $FF00 to $FFFF in the standard
64-Kbyte address space. Used only by hardware read/write commands.
0 = BDM resources not in map
1 = BDM resources in map
The bits in the BDM instruction register have the following meanings when a firmware command is ex-
ecuted.
H/F — Hardware/Firmware Flag
0 = Firmware control logic
1 = Hardware control logic
DATA — Data Flag
0 = No data
1 = Data included in command
R/W — Read/Write Flag
0 = Write
1 = Read
TTAGO — Trace, Tag, Go Field
REGN — Register/Next Field
Indicates which register is being affected by a command. In the case of a READ_NEXT or
WRITE_NEXT command, index register X is pre-incremented by two and the word pointed to by X is
then read or written.
INSTRUCTION — BDM Instruction Register (firmware command bit explanation) (BDM) $FF00
Bit 7 6 5 4 3 2 1 Bit 0
H/F DATA R/W TTAGO REGN
Table 45 TTAGO Decoding
TTAGO Value Instruction
00 —
01 GO
10 TRACE1
11 TAGGO
Table 46 REGN Decoding
REGN Value Instruction
000 —
001 —
010 READ/WRITE NEXT
011 PC
100 D
101 X
110 Y
111 SP