Siemens SAB 80515 Series User Manual page 43

On-Chip Peripheral Components
Figure 7-5 shows a functional diagram of a port latch with alternate function. To pass the alternate
function to the output pin and vice versa, however, the gate between the latch and driver circuit must
be open. Thus, to use the alternate input or output functions, the corresponding bit latch in the port
SFR has to contain a one (1); otherwise the pull-down FET is on and the port pin is stuck at 0. (This
does not apply to ports 1.0 to 1.3 when operated in compare output mode; refer to section 7.5.2 for
details). After reset all port latches contain ones (1).
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Figure 7-5
Port 1 and 3
Semiconductor Group 43