Block Guide — S12BDM V4

28

abort pulse could be used. After a command is aborted the target assumes the next negedge, after the abort

pulse, is the first bit of a new BDM command.

NOTE:

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.

Since the host knows the target serial clock frequency, the SYNC command (used to abort a command)

does not need to consider the lower possible target frequency. In this case, the host could issue a SYNC

very close to the 128 serial clock cycles length. Providing a small overhead on the pulse length in order to

assure the SYNC pulse will not be misinterpreted by the target. See 4.9 SYNC — Request Timed

Reference Pulse.

Figure 4-7 shows a SYNC command being issued after a READ_BYTE, which aborts the READ_BYTE

command. Note that, after the command is aborted a new command could be issued by the host computer.

Figure 4-7 ACK Abort Procedure at the Command Level

NOTE:

Figure 4-7 does not represent the signals in a true timing scale

Figure 4-8 shows a conflict between the ACK pulse and the SYNC request pulse. This conflict could

occur if a POD device is connected to the target BKGD pin and the target is already in debug active mode.

Consider that the target CPU is executing a pending BDM command at the exact moment the POD is being

connected to the BKGD pin. In this case, an ACK pulse is issued along with the SYNC command. In this

case, there is an electrical conflict between the ACK speedup pulse and the SYNC pulse. Since this is not

a probable situation, the protocol does not prevent this conflict from happening.

READ_BYTE

READ_STATUS

BKGD PIN

MEMORY ADDRESS

NEW BDM COMMAND

NEW BDM COMMAND

HOST

TARGET

HOST

TARGET

HOST

TARGET

SYNC RESPONSE

FROM THE TARGET

(OUT OF SCALE)

BDM DECODE

AND STARTS TO EXECUTES

THE READ_BYTE CMD

READ_BYTE CMD IS ABORTED

BY THE SYNC REQUEST

(OUT OF SCALE)