C517A_99 Datasheet, PDF (132/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
Write Sequence
The first and the last write operation in phase one are fixed for every calculation of the MDU. All
write operations inbetween determine the type of MDU calculation.
– A write-to-MD0 is the first transfer to be done in any case. This write resets the MDU and
triggers the error flag mechanism (see below).
– The next two or three write operations select the calculation type (32bit/16bit, 16bit/16bit,
16bit x 16bit)
The last write-to-MD5 finally starts the selected MUL/DIV operation
Read Sequence
– Any read-out of the MDx registers should begin with MD0
– The last read from MD5 (division) or MD3 (multiplication) determines the end of a whole
calculation and releases the error flag mechanism.
There is no restriction on the time within which a calculation must be completed. The CPU is allowed
to continue the program simultaneously to phase 2 and to fetch the result bytes at any time.
lf the user’s program takes care that interrupting a calculation is not possible, monitoring of the
calculation process is probably not needed. In this case, only the write sequence must be observed.
Any new write access to MD0 starts a new calculation, no matter whether the read-out of the former
result has been completed or not.
Semiconductor Group
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