Chapter 19 Background Debug Module (S12XBDMV2)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 767

19.1.2.3 Low-Power Modes

The BDM can be used until all bus masters (e.g., CPU or XGATE) are in stop mode. When CPU is in a
low power mode (wait or stop mode) all BDM firmware commands as well as the hardware
BACKGROUND command can not be used respectively are ignored. In this case the CPU can not enter
BDM active mode, and only hardware read and write commands are available. Also the CPU can not enter
a low power mode during BDM active mode.
If all bus masters are in stop mode, the BDM clocks are stopped as well. When BDM clocks are disabled
and one of the bus masters exits from stop mode the BDM clocks will restart and BDM will have a soft
reset (clearing the instruction register, any command in progress and disable the ACK function). The BDM
is now ready to receive a new command.
19.1.3 Block Diagram
A block diagram of the BDM is shown in Figure 19-1.
Figure 19-1. BDM Block Diagram
ENBDM
CLKSW
BDMACT
TRACE
SDV
16-Bit Shift Register
BKGD
Host
System Serial
Interface Data
Control
UNSEC
Register Block
Register
BDMSTS
Instruction Code
and
Execution
Standard BDM Firmware
LOOKUP TABLE
Secured BDM Firmware
LOOKUP TABLE
Bus Interface
and
Control Logic
Address
Data
Control
Clocks