C511_1 Datasheet, PDF (42/128 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Units
6.1.3 Alternate Functions
The pins of ports 1 and 3 are multifunctional. They are port pins and also serve to implement
alternate functions (special inputs/outputs for on-chip peripherals) as listed in table 6-6-3.
Figure 6-17a 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 pulldown FET is on and the port pin is stuck
at 0. After reset all port latches contain ones (1).
Read
Latch
Int. Bus
Write
to
Latch
Alternate
Output
Function
Q
D
&
Bit
Latch
Q
CLK
V_CC
Internal
Pull Up
Arrangement
Pin
Read
Pin
Figure 6-17a
Ports 1 and 3
Alternate
Input
Function
MCS01827
For port pins P1.2 to P1.5 different structures apply, see figures 6-17b and 6-17c.
Semiconductor Group
6-9