Freescale Semiconductor MCF51QE128RM manual ACK Abort Procedure at the Command Level

Models: MCF51QE128RM

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Chapter 18 Version 1 ColdFire Debug (CF1_DEBUG)

READ_MEM.B CMD

IS ABORTED BY THE SYNC REQUEST (NOT TO SCALE)

BKGD PIN

READ_MEM.B

 

 

ADDRESS[23-0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HOST

 

TARGET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SYNC RESPONSE FROM THE TARGET (NOT TO SCALE)

 

READ_XCSR_BYTE

 

 

NEW BDC COMMAND

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HOST

 

TARGET

 

 

HOST

 

TARGET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NEW BDC COMMAND

BDC DECODES

AND CPU TRYS TO EXECUTE

THE READ_MEM.B CMD

Figure 18-21. ACK Abort Procedure at the Command Level

Figure 18-22a 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 executing a BDC command. Consider that the target CPU is executing a pending BDC command at the exact moment the pod is being connected to the BKGD pin. In this case, an ACK pulse is issued at the same time as 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.

BDC CLOCK (TARGET MCU)

TARGET MCU DRIVES TO BKGD PIN

HOST DRIVES SYNC TO BKGD PIN

BKGD PIN

AT LEAST 128 CYCLES

ACK PULSE

HIGH-IMPEDANCE

ELECTRICAL CONFLICT

HOST AND TARGET

DRIVE TO BKGD PIN

HOST SYNC REQUEST PULSE

16 CYCLES

Figure 18-22. ACK Pulse and SYNC Request Conflict

SPEEDUP PULSE

The hardware handshake protocol is enabled by the ACK_ENABLE command and disabled by the ACK_DISABLE command. It also allows for pod devices to choose between the hardware handshake protocol or the software protocol that monitors the XCSR status byte. The ACK_ENABLE and ACK_DISABLE commands are:

ACK_ENABLE — Enables the hardware handshake protocol. The target issues the ACK pulse when a CPU command is executed. The ACK_ENABLE command itself also has the ACK pulse as a response.

MCF51QE128 MCU Series Reference Manual, Rev. 3

408

Freescale Semiconductor

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Freescale Semiconductor MCF51QE128RM manual ACK Abort Procedure at the Command Level