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User
’
s Manual
5-22
1999-08
The PEC response time is increased by all delays of the instructions in the pipeline that
are executed before starting the data transfer (including N).
When internal hold conditions between instruction pairs N-2/N-1 or N-1/N occur, the
minimum PEC response time may be extended by 1 state time for each of these
conditions.
When instruction N reads an operand from the internal code memory, or when N is a
call, return, trap, or MOV Rn, [Rm+ #data16] instruction, the minimum PEC response
time may additionally be extended by 2 state times during internal code memory
program execution.
In case instruction N reads the PSW and instruction N-1 has an effect on the condition
flags, the PEC response time may additionally be extended by 2 state times.
The worst case PEC response time during internal code memory program execution
adds to 9 state times (18 TCL).
Any reference to external locations increases the PEC response time due to pipeline
related access priorities. The following conditions have to be considered:
Instruction fetch from an external location
Operand read from an external location
Result write-back to an external location
Depending on where the instructions, source and destination operands are located,
there are a number of combinations. Note, however, that only access conflicts contribute
to the delay.
A few examples illustrate these delays:
The worst case interrupt response time including external accesses will occur, when
instructions N and N+1 are executed out of external memory, instructions N-1 and N
require external operand read accesses and instructions N-3, N-2 and N-1 write back
external operands. In this case the PEC response time is the time to perform 7 word
bus accesses.
When instructions N and N+1 are executed out of external memory, but all operands
for instructions N-3 through N-1 are in internal memory, then the PEC response time
is the time to perform 1 word bus access plus 2 state times.
Once a request for PEC service has been acknowledged by the CPU, the execution of
the next instruction is delayed by 2 state times plus the additional time it might take to
fetch the source operand from internal code memory or external memory and to write the
destination operand over the external bus in an external program environment.
Note: A bus access in this context includes all delays which can occur during an external
bus cycle.