Chapter 5 Background Debug Controller (S12ZBDCV2)
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
156
Freescale Semiconductor
Upon detecting the sync request from the host (which is a much longer low time than would ever occur
during normal BDC communications), the target:
1. Discards any incomplete command
2. Waits for BKGD to return to a logic high.
3. Delays 16 cycles to allow the host to stop driving the high speed-up pulse.
4. Drives BKGD low for 128 BDCSI clock cycles.
5. Drives a 1-cycle high speed-up pulse to force a fast rise time on BKGD.
6. Removes all drive to the BKGD pin so it reverts to high impedance.
7. Clears the OVRRUN flag (if set).
The host measures the low time of this 128-cycle SYNC response pulse and determines the correct speed
for subsequent BDC communications. Typically, the host can determine the correct communication speed
within a few percent of the actual target speed and the serial protocol can easily tolerate this speed error.
If the SYNC request is detected by the target, any partially executed command is discarded. This is referred
to as a soft-reset, equivalent to a timeout in the serial communication. After the SYNC response, the target
interprets the next negative edge (issued by the host) as the start of a new BDC command or the start of
new SYNC request.
A SYNC command can also be used to abort a pending ACK pulse. This is explained in
.
5.4.4.2
ACK_DISABLE
Disables the serial communication handshake protocol. The subsequent commands, issued after the
ACK_DISABLE command, do not execute the hardware handshake protocol. This command is not
followed by an ACK pulse.
5.4.4.3
ACK_ENABLE
Enables the hardware handshake protocol in the serial communication. The hardware handshake is
implemented by an acknowledge (ACK) pulse issued by the target MCU in response to a host command.
The ACK_ENABLE command is interpreted and executed in the BDC logic without the need to interface
Disable host/target handshake protocol
Always Available
0x03
host
target
D
L
Y
Enable host/target handshake protocol
Always Available
0x02
host
target
D
A
C
K
