mc9s12c32mpb16 Freescale Semiconductor, Inc, mc9s12c32mpb16 Datasheet - Page 187

• Manufacturer Part Number: mc9s12c32mpb16
• Description: Hcs12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

6.4.9
The SYNC command is unlike other BDM commands because the host does not necessarily know the
correct communication speed to use for BDM communications until after it has analyzed the response to
the SYNC command. To issue a SYNC command, the host should perform the following steps:
Upon detecting the SYNC request from the host, the target performs the following steps:
The host measures the low time of this 128 cycle SYNC response pulse and determines the correct speed
for subsequent BDM communications. Typically, the host can determine the correct communication speed
within a few percent of the actual target speed and the communication protocol can easily tolerate speed
errors of several percent.
As soon as the SYNC request is detected by the target, any partially received command or bit retrieved is
discarded. This is referred to as a soft-reset, equivalent to a time-out in the serial communication. After the
SYNC response, the target will consider the next falling edge (issued by the host) as the start of a new
BDM command or the start of new SYNC request.
Another use of the SYNC command pulse is to abort a pending ACK pulse. The behavior is exactly the
same as in a regular SYNC command. Note that one of the possible causes for a command to not be
acknowledged by the target is a host-target synchronization problem. In this case, the command may not
have been understood by the target and so an ACK response pulse will not be issued.
6.4.10
When a TRACE1 command is issued to the BDM in active BDM, the CPU exits the standard BDM
firmware and executes a single instruction in the user code. As soon as this has occurred, the CPU is forced
to return to the standard BDM firmware and the BDM is active and ready to receive a new command. If
the TRACE1 command is issued again, the next user instruction will be executed. This facilitates stepping
or tracing through the user code one instruction at a time.
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1. Drive the BKGD pin low for at least 128 cycles at the lowest possible BDM serial communication
2. Drive BKGD high for a brief speedup pulse to get a fast rise time (this speedup pulse is typically
3. Remove all drive to the BKGD pin so it reverts to high impedance.
4. Listen to the BKGD pin for the sync response pulse.
1. Discards any incomplete command received or bit retrieved.
2. Waits for BKGD to return to a logic 1.
3. Delays 16 cycles to allow the host to stop driving the high speedup pulse.
4. Drives BKGD low for 128 cycles at the current BDM serial communication frequency.
5. Drives a one-cycle high speedup pulse to force a fast rise time on BKGD.
6. Removes all drive to the BKGD pin so it reverts to high impedance.
frequency (the lowest serial communication frequency is determined by the crystal oscillator or the
clock chosen by CLKSW.)
one cycle of the host clock.)
SYNC — Request Timed Reference Pulse
Instruction Tracing
MC9S12C-Family / MC9S12GC-Family
Rev 01.23
Chapter 6 Background Debug Module (BDMV4) Block Description
187