MC9S12E256 Datasheet, PDF (446/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 15 Background Debug Module (BDMV4)
15.1.1 Features
• Single-wire communication with host development system
• BDMV4 (and BDM2): Enhanced capability for allowing more flexibility in clock rates
• BDMV4: SYNC command to determine communication rate
• BDMV4: GO_UNTIL command
• BDMV4: Hardware handshake protocol to increase the performance of the serial communication
• Active out of reset in special single-chip mode
• Nine hardware commands using free cycles, if available, for minimal CPU intervention
• Hardware commands not requiring active BDM
• 15 firmware commands execute from the standard BDM firmware lookup table
• Instruction tagging capability
• Software control of BDM operation during wait mode
• Software selectable clocks
• When secured, hardware commands are allowed to access the register space in special single-chip
mode, if the FLASH and EEPROM erase tests fail.
15.1.2 Modes of Operation
BDM is available in all operating modes but must be enabled before firmware commands are executed.
Some system peripherals may have a control bit which allows suspending the peripheral function during
background debug mode.
15.1.2.1 Regular Run Modes
All of these operations refer to the part in run mode. The BDM does not provide controls to conserve power
during run mode.
• Normal operation
General operation of the BDM is available and operates the same in all normal modes.
• Special single-chip mode
In special single-chip mode, background operation is enabled and active out of reset. This allows
programming a system with blank memory.
• Special peripheral mode
BDM is enabled and active immediately out of reset. BDM can be disabled
by clearing the BDMACT bit in the BDM status (BDMSTS) register. The
BDM serial system should not be used in special peripheral mode.
• Emulation modes
General operation of the BDM is available and operates the same as in normal modes.
MC9S12E256 Data Sheet, Rev. 1.08
446
Freescale Semiconductor