S912XEG128J2MAA Datasheet, PDF (284/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 7 Background Debug Module (S12XBDMV2)
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 firmware 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 firmware 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 firmware write commands,
should only be altered by the BDM hardware or standard firmware lookup table as part of BDM
command execution.
Table 7-3. BDMSTS Field Descriptions
Field
7
ENBDM
6
BDMACT
4
SDV
3
TRACE
Description
Enable BDM — This bit controls whether the BDM is enabled or disabled. When enabled, BDM can be made
active to allow firmware 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 firmware 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 firmware 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.
BDM Active Status — This bit becomes set upon entering BDM. The standard BDM firmware lookup table is
then enabled and put into the memory map. BDMACT is cleared by a carefully timed store instruction in the
standard BDM firmware 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
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 firmware or hardware read command or after data has been received as part of a firmware 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 firmware to control program flow execution.
0 Data phase of command not complete
1 Data phase of command is complete
TRACE1 BDM Firmware Command is Being Executed — This bit gets set when a BDM TRACE1 firmware
command is first recognized. It will stay set until BDM firmware 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
MC9S12XE-Family Reference Manual Rev. 1.25
284
Freescale Semiconductor