4Data Transfer
4 – 11
stored to the 8 lower bits of the memory word.
From the DMD bus, the PX register may be:
1. Loaded with a data move instruction, explicitly specifying the PX
register as the destination. The lower 8 bits of the data value are used
and the upper 8 are discarded.
PX = AX0;
2. Read with a data move instruction, explicitly specifying the PX register
as a source. The upper 8 bits of the value read from the register are all
zeroes.
AX0 = PX;
Whenever any register is written out to program memory, the source
register supplies the upper 16 bits. The contents of the PX register are
automatically added as the lower 8 bits. If these lower 8 bits of data to be
transferred to program memory (through the PMD bus) are important,
you should load the PX register from DMD bus before the program
memory write operation.
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