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USING ST62xx I/O PORTS SAFELY

Table 3. Example of a SET sequence with RAM buffer for DR

Such a sequence is only required for DR address when some bits are set to input. No restric-

tions apply for operating on OR or DDR.

It is recommended that the OR should be used primarily for switching of pin input operating

modes. This register switches the port bits from input without pull-up to analog input, or

switches from input mode with pull-up to interrupt input with pull-up. Transition diagrams

showing the optimum coding sequence for modifying the states are shown in the following fig-

ures.

DRA

.def 00ch, 0ffh, 0ffh ; DR of IOP3

DRBUFF

.def 090h, 0ffh, 0ffh ; buffer for IOP3 DR

...

SET 2, DRBUFF

LD A, DRBUFF

LD DRA, A

...