CENTRAL PROCESSING UNIT
M68HC16 Z SERIES
4-44
USER’S MANUAL
4.14.4.6 BDM Serial Interface
The BDM serial interface uses a synchronous protocol similar to that of the
Freescale
serial peripheral interface (SPI).
is a diagram of the serial logic required to
use BDM with a development system.
Figure 4-7 BDM Serial I/O Block Diagram
The development system serves as the master of the serial link, and is responsible for
the generation of the serial interface clock signal (DSCLK).
Serial clock frequency range is from DC to one-half the CPU16 clock frequency. If
DSCLK is derived from the CPU16 system clock, development system serial logic can
be synchronized with the target processor.
The serial interface operates in full-duplex mode. Data transfers occur on the falling
edge of DSCLK and are stable by the following rising edge of DSCLK. Data is trans-
mitted MSB first, and is latched on the rising edge of DSCLK.
The serial data word is 17 bits wide, which includes 16 data bits and a status/control
bit. Bit 16 indicates status of CPU-generated messages.
Command and data transfers initiated by the development system must clear bit 16.
All commands that return a result return 16 bits of data plus one status bit.
CONTROL
LOGIC
SERIAL IN
PARALLEL OUT
PARALLEL IN
SERIAL OUT
EXECUTION
UNIT
STATUS
SYNCHRONIZE
MICROSEQUENCER
PARALLEL IN
SERIAL OUT
SERIAL IN
PARALLEL OUT
RESULT LATCH
CONTROL
LOGIC
STATUS
DATA
DSI
DSO
DSCLK
SERIAL
CLOCK
16
16
RCV DATA LATCH
CPU
INSTRUCTION
REGISTER BUS
16
COMMAND LATCH
DATA
16
DEVELOPMENT SYSTEM
0
BDM SER
COM BLOCK
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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