M68HC16 Z SERIES
CENTRAL PROCESSING UNIT
USER’S MANUAL
4-43
of BKPT or execution of the BGND instruction. IPIPE0 and IPIPE1 change function be-
fore 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 before initiation of normal bus cycles. IPIPE0 and IPIPE1 are valid
when normal instruction prefetch begins.
4.14.4.4 BDM Commands
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 corresponding to a command is executed as soon as the com-
mand is complete. Result operands are loaded into the output shift register to be shift-
ed out as the next command is read. This process is repeated for each command until
the CPU returns to normal operating mode. The BDM command set is summarized in
. Refer to the
CPU16 Reference Manual (CPU16RM/AD) for a BDM com-
mand glossary.
4.14.4.5 Returning from BDM
BDM is terminated when a resume execution (GO) command is received. GO refills
the instruction pipeline from address (PK : PC – $0006). FREEZE is negated before
the first prefetch. Upon negation of FREEZE, the BDM serial subsystem is disabled
and the DSO/DSI signals revert to IPIPE0/IPIPE1 functionality.
Table 4-7 Command Summary
Command
Mnemonic
Description
Read Registers
from Mask
RREGM
Read contents of registers specified by command
word register mask
Write Registers
from Mask
WREGM
Write to registers specified by command word
register mask
Read MAC Registers
RDMAC
Read contents of entire multiply and accumulate
register set
Write MAC Registers
WRMAC
Write to entire multiply and accumulate register set
Read PC and SP
RPCSP
Read contents of program counter and stack pointer
Write PC and SP
WPCSP
Write to program counter and stack pointer
Read Data Memory
RDMEM
Read byte from specified 20-bit address in data
space
Write Data Memory
WDMEM
Write byte to specified 20-bit address in data space
Read Program Memory
RPMEM
Read word from specified 20-bit address in program
space
Write Program Memory
WPMEM
Write word to specified 20-bit address in program
space
Execute from Current
PK : PC
GO
Instruction pipeline flushed and refilled; instructions
executed from current PC – $0006
Null Operation
NOP
Null command performs no operation
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