MOTOROLA
10-18
DEVELOPMENT SUPPORT
CPU16
REFERENCE MANUAL
Figure 10-14 BKPT/DSCLK Logic Diagram
Since it is not latched, BKPT_TAG must be synchronized with CPU16 bus cycles. If
negation of BKPT_TAG extends past FREEZE assertion, the CPU16 will clock on it as
though it were the first DSCLK pulse.
DSCLK is the gated serial clock. Normally high, it pulses low for each bit transferred.
At the end of the seventeenth clock period, it remains high until the start of the next
transmission. Clock frequency is implementation dependent and may range from dc
to the maximum specified frequency.
10.4.8 BDM Command Format
The following standard bit format is utilized by all BDM commands.
Operation Word
All commands have a unique 16-bit operation word. No command requires an exten-
sion word to specify the operation to be performed.
Extension Words
Some commands require extension words for addresses or immediate data. Address-
es require two extension words to accommodate 20 bits. Immediate data can be either
one or two words in length — byte and word data each require a single extension word,
long-word data requires two words. Both operands and addresses are transferred
most significant word first.
10.4.9 Command Sequence Diagram
A command sequence diagram illustrates the serial bus traffic for each command.
Each bubble in the diagram represents a single 17-bit transfer across the bus. The top
half of each bubble shows data sent from the development system to the CPU16. The
bottom half shows data returned by the CPU16 in response to commands. Transmis-
sions overlap to minimize latency.
15
0
OPERATION WORD
EXTENSION WORD(S)
RESET
BKPT/DSCLK
BKPT_TAG
SHIFT_CLK
FORCE_BGND
S1
S2
R
Q
Q
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.