C517A_99 Datasheet, PDF (135/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
Please note that the error flag mechanism is just an option to monitor the MDU operation. lf the
user’s program is designed such that an MDU operation cannot be interrupted by other calculations,
then there is no need to pay attention to the error flag. In this case it is also possible to change the
order in which the MDx registers are read, or even to skip some register read instructions.
Concerning the shift or normalize instructions, it is possible to read the result before the complete
execution time of six machine cycles has passed (e.g. when a small number of shifts has been
programmed). All of the above "illegal" actions would set the error flag, but on the other hand do not
affect a correct MDU operation. The user has just to make sure that everything goes right.
The error flag (MDEF) is located in ARCON and can be read only. lt is automatically cleared after
being read.
Semiconductor Group
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