Block Guide — S12BDM V4

29

Figure 4-8 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.

The commands are described as follows:

•

ACK_ENABLE — enables the hardware handshake protocol. The target will issue the ACK pulse

when a CPU command is executed by the CPU. The ACK_ENABLE command itself also has the

ACK pulse as a response.

•

ACK_DISABLE — disables the ACK pulse protocol. In this case, the host needs to use the worst

case delay time at the appropriate places in the protocol.

The default state of the BDM after reset is hardware handshake protocol disabled.

All the read commands will ACK (if enabled) when the data bus cycle has completed and the data is then

ready for reading out by the BKGD serial pin. All the write commands will ACK (if enabled) after the data

has been received by the BDM through the BKGD serial pin and when the data bus cycle is complete. See

4.3 BDM Hardware Commands and 4.4 Standard BDM Firmware Commands for more information

on the BDM commands.

BDM CLOCK

(TARGET MCU)

TARGET MCU

DRIVES TO

BKGD PIN

BKGD PIN

16 CYCLES

SPEEDUP PULSE

HIGH-IMPEDANCE

HOST

DRIVES SYNC

TO BKGD PIN

ACK PULSE

HOST SYNC REQUEST PULSE

AT LEAST 128 CYCLES

ELECTRICAL CONFLICT

HOST AND

TARGET DRIVE

TO BKGD PIN