Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256 用户手册

Freescale Semiconductor

201

The BDM can be used until all bus masters (e.g., CPU or XGATE or others depending on which masters
are available on the SOC) 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.

A block diagram of the BDM is shown in

.

A single-wire interface pin called the background debug interface (BKGD) pin is used to communicate
with the BDM system. During reset, this pin is a mode select input which selects between normal and
special modes of operation. After reset, this pin becomes the dedicated serial interface pin for the
background debug mode.

ENBDM

CLKSW

BDMACT

TRACE

SDV

16-Bit Shift Register

BKGD

Host

System

Serial

Interface

Data

Control

UNSEC

Register Block

Instruction Code

and

Execution

Standard BDM Firmware

LOOKUP TABLE

Secured BDM Firmware

LOOKUP TABLE

Bus Interface

and

Control Logic

Address

Data

Control

Clocks