Datasheet

Chapter 5. Debug Support 5-29
Background Debug Mode (BDM)
Figure 5-19. 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.
NOTE:
A not-ready response can be ignored except during a
memory-referencing cycle. Otherwise, the debug module can
accept a new serial transfer after 32 processor clock periods.
• In cycle 3, the development system supplies the low-order 16 address bits. The
debug module always returns a not-ready response.
• At the completion of cycle 3, the debug module initiates a memory read operation.
Any serial transfers that begin during a memory access return a not-ready response.
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
SEQUENCE TAKEN IF
OPERATION HAS NOT
COMPLETED
DATA UNUSED FROM
THIS TRANSFER
SEQUENCE TAKEN IF
ILLEGAL COMMAND
IS RECEIVED BY DEBUG MODULE
RESULTS FROM PREVIOUS COMMAND
RESPONSES FROM THE DEBUG MODULE
NONSERIAL-RELATED ACTIVITY
MS ADDR
"NOT READY"
XXX
"ILLEGAL"
LS ADDR
"NOT READY"
NEXT CMD
"NOT READY"
READ (LONG)
???
NEXT CMD
"NOT READY"
XXX
"NOT READY"
XXXXX
XXX
BERR
MS RESULT
NEXT CMD
LS RESULT
READ
MEMORY
LOCATION
NEXT
COMMAND
CODE
SEQUENCE TAKEN IF BUS
ERROR OCCURS ON
MEMORY ACCESS
HIGH- AND LOW-ORDER
16 BITS OF RESULT
XXX