
CPU16
REFERENCE MANUAL
DEVELOPMENT SUPPORT
MOTOROLA
10-19
Figure 10-15
shows an example command sequence diagram. A description of the in-
formation in the diagram follows.
Figure 10-15 Command Sequence Diagram Example
The cycle in which the command is issued contains the command word (RPMEM).
During the same cycle, the CPU16 responds with either the low order results of the
previous command or with a command complete status if no results were required.
During the second cycle, the development system supplies the 4 high-order bits of a
memory address. The CPU16 returns a NOT READY response unless the received
command was decoded as unimplemented, in which case the response is the ILLE-
GAL command encoding. When an ILLEGAL response occurs, the development sys-
tem must retransmit the command.
In the third cycle, the development system supplies the 16 low-order bits of the mem-
ory address. The CPU16 always returns a NOT READY response in this cycle. At the
completion of the third cycle, the CPU16 initiates a memory read operation. Any serial
transfers that begin while the memory access is in progress return the NOT READY
response.
Results are returned in the serial transfer cycle following completion of the memory ac-
cess. If the serial clock is slow, there may be additional NOT READY responses from
the CPU16. The data transmitted to the CPU during the final transfer is the next com-
mand word.
NEXT
COMMAND
CODE
NEXT CMD
RESULT
NOT USED
NOT READY
SEQUENCE TAKEN
WHEN OPERATION
IS NOT COMPLETE
COMMAND
EXECUTION
16 LSB OF
ADDRESS
4 MSB OF
ADDRESS
READ
MEMORY
LOCATION
*RESULTS OF PREVIOUS COMMAND
OR COMMAND COMPLETE STATUS
COMMAND
TRANSMITTED
THIS CYCLE
LS ADDR
NOT READY
NEXT CMD
NOT READY
SEQUENCE TAKEN WHEN
AN ILLEGAL COMMAND
IS RECEIVED
RESPONSES FROM
THE CPU16
MS ADDR
NOT READY
NOT USED
ILLEGAL
RPMEM
*
COMMANDS
TRANSMITTED TO
THE CPU16
F
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