MC9S12KG128 Datasheet, PDF (465/600 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 15 Background Debug Module (BDMV4)
READ_BYTE CMD IS ABORTED
BY THE SYNC REQUEST
(OUT OF SCALE)
SYNC RESPONSE
FROM THE TARGET
(OUT OF SCALE)
BKGD PIN
READ_BYTE
MEMORY ADDRESS
HOST TARGET
READ_STATUS
HOST TARGET
NEW BDM COMMAND
HOST TARGET
BDM DECODE
AND STARTS TO EXECUTES
THE READ_BYTE CMD
NEW BDM COMMAND
Figure 15-12. ACK Abort Procedure at the Command Level
Figure 15-13 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. Because this is
not a probable situation, the protocol does not prevent this conflict from happening.
BDM CLOCK
(TARGET MCU)
TARGET MCU
DRIVES TO
BKGD PIN
HOST
DRIVES SYNC
TO BKGD PIN
BKGD PIN
AT LEAST 128 CYCLES
ACK PULSE
HOST AND
TARGET DRIVE
TO BKGD PIN
HOST SYNC REQUEST PULSE
HIGH-IMPEDANCE
ELECTRICAL CONFLICT
SPEEDUP PULSE
16 CYCLES
Figure 15-13. ACK Pulse and SYNC Request Conflict
NOTE
This information is being provided so that the MCU integrator will be aware
that such a conflict could eventually occur.
The hardware handshake protocol is enabled by the ACK_ENABLE and disabled by the ACK_DISABLE
BDM commands. This provides backwards compatibility with the existing POD devices which are not
able to execute the hardware handshake protocol. It also allows for new POD devices, that support the
hardware handshake protocol, to freely communicate with the target device. If desired, without the need
for waiting for the ACK pulse.
MC9S12KG128 Data Sheet, Rev. 1.15
Freescale Semiconductor
465