Datasheet

Development Support
MC68HC812A4 Data Sheet, Rev. 7
218 Freescale Semiconductor
17.4.1.2 Firmware Command
The bits in the BDM instruction register have the following meanings when a firmware command is
executed.
H/F — Hardware/Firmware Flag
1 = Hardware control logic
0 = Firmware control logic
DATA — Data Flag
1 = Data included in command
0 = No data
R/W — Read/Write Flag
1 = Read
0 = Write
TTAGO — Trace, Tag, and 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 2 and the word pointed to by X is then
read or written.
Address: $FF00
Bit 7654321Bit 0
Read:
H/F DATA R/W TTAGO REGN
Write:
Reset:00000000
Figure 17-5. BDM Instruction Register (INSTRUCTION)
Table 17-4. TTAGO Decoding
TTAGO Value Instruction
00 —
01 GO
10 TRACE1
11 TAGGO
Table 17-5. REGN Decoding
REGN Value Instruction
000 —
001 —
010 READ/WRITE NEXT
011 PC
100 D
101 X
110 Y
111 SP