
Debug Support
MCF5271 Reference Manual, Rev. 2
30-22
Freescale Semiconductor
Operands and addresses are transferred most-significant word first. In the following descriptions
of the BDM command set, the optional set of extension words is defined as address, data, or
operand data.
30.5.3.2 Command Sequence Diagrams
The command sequence diagram in
Figure 30-16 shows serial bus traffic for commands. Each
bubble represents a 17-bit bus transfer. The top half of each bubble indicates the data the
development system sends to the debug module; the bottom half indicates the debug module’s
response to the previous development system commands. Command and result transactions
overlap to minimize latency.
Figure 30-16. Command Sequence Diagram
The sequence is as follows:
In cycle 1, the development system command is issued (READ in this example). The debug
module responds with either the low-order results of the previous command or a command
complete status of the previous command, if no results are required.
In cycle 2, the development system supplies the high-order 16 address bits. The debug
module returns a not-ready response unless the received command is decoded as
unimplemented, which is indicated by the illegal command encoding. If this occurs, the
development system should retransmit the command.
XXX
’NOT READY’
READ (LONG)
???
MS ADDR
’NOT READY’
LS ADDR
’NOT READY’
NEXT CMD
’NOT READY’
NEXT CMD
’NOT READY’
NEXT CMD
LS RESULT
Commands transmitted to the debug module
Command code transmitted during this cycle
High-order 16 bits of memory address
Low-order 16 bits of memory address
Non-serial-related
Next
Command
Code
Sequence taken if operation
has not completed
activity
READ
MEMORY
LOCATION
XXX
BERR
XXX
MS RESULT
XXX
’ILLEGAL’
Responses from the debug module
Results from previous command
Sequence taken if illegal command
is received by debug module
Data used from this transfer
Sequence taken if bus error
occurs on memory access
High- and low-order 16 bits of result