Chapter 7 Background Debug Module (S12XBDMV2)
MC9S12XE-Family Reference Manual , Rev. 1.21
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Read: All modes through BDM operation when not secured
Write: All modes through BDM operation when not secured, but subject to the following:
— ENBDM should only be set via a BDM hardware command if the BDM rmware commands
are needed. (This does not apply in special single chip and emulation modes).
— BDMACT can only be set by BDM hardware upon entry into BDM. It can only be cleared by
the standard BDM rmware lookup table upon exit from BDM active mode.
— CLKSW can only be written via BDM hardware WRITE_BD commands.
— All other bits, while writable via BDM hardware or standard BDM rmware write commands,
should only be altered by the BDM hardware or standard rmware lookup table as part of BDM
command execution.
Table 7-3. BDMSTS Field Descriptions
Field
Description
7
ENBDM
Enable BDM — This bit controls whether the BDM is enabled or disabled. When enabled, BDM can be made
active to allow rmware commands to be executed. When disabled, BDM cannot be made active but BDM
hardware commands are still allowed.
0 BDM disabled
1 BDM enabled
Note: ENBDM is set by the rmware out of reset in special single chip mode. In emulation modes (if modes
available) the ENBDM bit is set by BDM hardware out of reset. In special single chip mode with the device
secured, this bit will not be set by the rmware until after the non-volatile memory erase verify tests are
complete. In emulation modes (if modes available) with the device secured, the BDM operations are
blocked.
6
BDMACT
BDM Active Status — This bit becomes set upon entering BDM. The standard BDM rmware lookup table is
then enabled and put into the memory map. BDMACT is cleared by a carefully timed store instruction in the
standard BDM rmware as part of the exit sequence to return to user code and remove the BDM memory from
the map.
0 BDM not active
1 BDM active
4
SDV
Shift Data Valid — This bit is set and cleared by the BDM hardware. It is set after data has been transmitted as
part of a rmware or hardware read command or after data has been received as part of a rmware or hardware
write command. It is cleared when the next BDM command has been received or BDM is exited. SDV is used
by the standard BDM rmware to control program ow execution.
0 Data phase of command not complete
1 Data phase of command is complete
3
TRACE
TRACE1 BDM Firmware Command is Being Executed — This bit gets set when a BDM TRACE1 rmware
command is rst recognized. It will stay set until BDM rmware is exited by one of the following BDM commands:
GO or GO_UNTIL.
0 TRACE1 command is not being executed
1 TRACE1 command is being executed