HCS08 datasheet(239/290 Pages) MOTOROLA

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Data Sheet — MC9S08GB60/D V1.5

MOTOROLA

239

MC9S08GB/GT

15.3 Background Debug Controller (BDC)

All MCUs in the HCS08 Family contain a single-wire background debug interface which supports

in-circuit programming of on-chip nonvolatile memory and sophisticated non-intrusive debug capabilities.

Unlike debug interfaces on earlier 8-bit MCUs, this system does not interfere with normal application

resources. It does not use any user memory or locations in the memory map and does not share any on-chip

peripherals.

BDC commands are divided into two groups:

•

Active background mode commands require that the target MCU is in active background mode (the

user program is not running). Active background mode commands allow the CPU registers to be

read or written, and allow the user to trace one user instruction at a time, or GO to the user program

from active background mode.

•

Non-intrusive commands can be executed at any time even while the user’s program is running.

Non-intrusive commands allow a user to read or write MCU memory locations or access status and

control registers within the background debug controller.

Typically, a relatively simple interface pod is used to translate commands from a host computer into

commands for the custom serial interface to the single-wire background debug system. Depending on the

development tool vendor, this interface pod may use a standard RS232 serial port, a parallel printer port,

or some other type of communications such as a universal serial bus (USB) to communicate between the

host PC and the pod. The pod typically connects to the target system with ground, the BKGD pin, RESET,

and sometimes VDD. An open-drain connection to reset allows the host to force a target system reset which

is useful to regain control of a lost target system or to control startup of a target system before the on-chip

nonvolatile memory has been programmed. Sometimes VDD can be used to allow the pod to use power

from the target system to avoid the need for a separate power supply. However, if the pod is powered

separately, it can be connected to a running target system without forcing a target system reset or otherwise

disturbing the running application program.

Figure 15-1 BDM Tool Connector

15.3.1 BKGD Pin Description

BKGD is the single-wire background debug interface pin. The primary function of this pin is for

bidirectional serial communication of active background mode commands and data. During reset, this pin

is used to select between starting in active background mode or starting the user’s application program.

This pin is also used to request a timed sync response pulse to allow a host development tool to determine

the correct clock frequency for background debug serial communications.

BDC serial communications use a custom serial protocol first introduced on the M68HC12 Family of

microcontrollers. This protocol assumes the host knows the communication clock rate which is determined

NO CONNECT 5

NO CONNECT 3

RESET

BKGD

GND

VDD

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