
MOTOROLA
10-12
DEVELOPMENT SUPPORT
CPU16
REFERENCE MANUAL
10.4.4 Entering BDM
When the processor detects a breakpoint or decodes a BGND instruction, it suspends
instruction execution and asserts the FREEZE output. Once FREEZE has been as-
serted, the CPU enables the serial communication hardware and awaits a command.
Assertion of FREEZE causes opcode tracking signals IPIPE0 and IPIPE1 to change
definition and become serial communication signals DSO and DSI. FREEZE is assert-
ed at the next instruction boundary after BKPT is asserted. IPIPE0 and IPIPE1 change
function before an EXCEPTION signal can be generated. The development system
must use FREEZE assertion as an indication that BDM has been entered. When BDM
is exited, FREEZE is negated prior to initiation of normal bus cycles — IPIPE0 and
IPIPE1 will be valid when normal instruction prefetch begins.
10.4.5 Command Execution
Figure 10-8
summarizes BDM command execution. Commands consist of one 16-bit
operation word and can include one or more 16-bit extension words. Each incoming
word is read as it is assembled by the serial interface. The microcode routine corre-
sponding to a command is executed as soon as the command is complete. Result op-
erands are loaded into the output shift register to be shifted out as the next command
is read. This process is repeated for each command until the CPU returns to normal
operating mode.
Table 10-3 BDM Signals
State
Signal Name
BKPT
IPIPE0
IPIPE1
DSCLCK
DSO
DSI
Type
Input
Output
Output
Input
Output
Input
Description
No Background Mode
Signals breakpoint to CPU16
Shows instruction pipeline state
Shows instruction pipeline state
BDM serial clock
BDM serial output
BDM serial input
Background Mode
F
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