MC9S12G FREESCALE [Freescale Semiconductor, Inc], MC9S12G Datasheet - Page 272

• Manufacturer Part Number: MC9S12G
• Description: Ignores external trigger. Performs one conversion sequence and stops.
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Background Debug Module (S12SBDMV1)
7.4.8
The abort procedure is based on the SYNC command. In order to abort a command, which had not issued
the corresponding ACK pulse, the host controller should generate a low pulse in the BKGD pin by driving
it low for at least 128 serial clock cycles and then driving it high for one serial clock cycle, providing a
speedup pulse. By detecting this long low pulse in the BKGD pin, the target executes the SYNC protocol,
see
and therefore the related ACK pulse, are being aborted. Therefore, after the SYNC protocol has been
completed the host is free to issue new BDM commands. For BDM firmware READ or WRITE commands
it can not be guaranteed that the pending command is aborted when issuing a SYNC before the
corresponding ACK pulse. There is a short latency time from the time the READ or WRITE access begins
until it is finished and the corresponding ACK pulse is issued. The latency time depends on the firmware
READ or WRITE command that is issued and on the selected bus clock rate. When the SYNC command
starts during this latency time the READ or WRITE command will not be aborted, but the corresponding
ACK pulse will be aborted. A pending GO, TRACE1 or GO_UNTIL command can not be aborted. Only
the corresponding ACK pulse can be aborted by the SYNC command.
Although it is not recommended, the host could abort a pending BDM command by issuing a low pulse in
the BKGD pin shorter than 128 serial clock cycles, which will not be interpreted as the SYNC command.
The ACK is actually aborted when a negative edge is perceived by the target in the BKGD pin. The short
abort pulse should have at least 4 clock cycles keeping the BKGD pin low, in order to allow the negative
edge to be detected by the target. In this case, the target will not execute the SYNC protocol but the pending
command will be aborted along with the ACK pulse. The potential problem with this abort procedure is
when there is a conflict between the ACK pulse and the short abort pulse. In this case, the target may not
perceive the abort pulse. The worst case is when the pending command is a read command (i.e.,
READ_BYTE). If the abort pulse is not perceived by the target the host will attempt to send a new
command after the abort pulse was issued, while the target expects the host to retrieve the accessed
memory byte. In this case, host and target will run out of synchronism. However, if the command to be
aborted is not a read command the short abort pulse could be used. After a command is aborted the target
assumes the next negative edge, after the abort pulse, is the first bit of a new BDM command.
272
Section 7.4.9, “SYNC — Request Timed Reference
This document is valid for the S12G96 and the S12G128 device. All information related to other devices is preliminary.
Hardware Handshake Abort Procedure
The ACK pulse does not provide a time out. This means for the GO_UNTIL
command that it can not be distinguished if a stop or wait has been executed
(command discarded and ACK not issued) or if the “UNTIL” condition
(BDM active) is just not reached yet. Hence in any case where the ACK
pulse of a command is not issued the possible pending command should be
aborted before issuing a new command. See the handshake abort procedure
described in
The details about the short abort pulse are being provided only as a reference
for the reader to better understand the BDM internal behavior. It is not
recommended that this procedure be used in a real application.
Section 7.4.8, “Hardware Handshake Abort
MC9S12G Family Reference Manual,
NOTE
NOTE
Pulse”, and assumes that the pending command
Rev.1.01
Procedure”.
Freescale Semiconductor