PC912XDP512F0MPVR datasheet(583/1348 Pages) FREESCALE

583 / 1348 page

Chapter 15 Background Debug Module (S12XBDMV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

583

The external host should wait at least for 76 bus clock cycles after a TRACE1 or GO command before

starting any new serial command. This is to allow the CPU to exit gracefully from the standard BDM

ﬁrmware lookup table and resume execution of the user code. Disturbing the BDM shift register

prematurely may adversely affect the exit from the standard BDM ﬁrmware lookup table.

NOTE

If the bus rate of the target processor is unknown or could be changing or the

external wait function is used, it is recommended that the ACK

(acknowledge function) is used to indicate when an operation is complete.

When using ACK, the delay times are automated.

Figure 15-7 represents the BDM command structure. The command blocks illustrate a series of eight bit

times starting with a falling edge. The bar across the top of the blocks indicates that the BKGD line idles

in the high state. The time for an 8-bit command is 8

× 16 target clock cycles.1

Figure 15-7. BDM Command Structure

1. Target clock cycles are cycles measured using the target MCU’s serial clock rate. See Section 15.4.6, “BDM Serial Interface”

and Section 15.3.2.1, “BDM Status Register (BDMSTS)” for information on how serial clock rate is selected.

Hardware

Firmware

GO,

48-BC

BC = Bus Clock Cycles

Command

Address

150-BC

Delay

DELAY

8 Bits

AT ~16 TC/Bit

16 Bits

AT ~16 TC/Bit

16 Bits

AT ~16 TC/Bit

Command

Address

Data

Read

Write

Read

Write

TRACE

Command

Data

76-BC

Delay

Command

150-BC

Delay

36-BC

DELAY

Command

Data

Command

TC = Target Clock Cycles

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