C515C_9711 Datasheet, PDF (79/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.1.2 Alternate Functions of Ports
Several pins of ports 1, 3, 4, and 7 are multifunctional. They are port pins and also serve to
implement special features as listed in table 6-1. The SSC interface pins of port 4 are described in
a previous section 6.1.1.2.4.
Figure 6-13 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 operating in compare output mode). 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
Alternate
Input
Function
MCS01827
Figure 6-13
Circuitry of Ports 1, 3, 4 and 7
Port 5 has no alternate functions as described above. Therefore, the port circuitry has no switching
capability between alternate function and normal I/O operation. This more simple circuitry is shown
as basic port structure in figure 6-3.
The two CAN controller transmit/receive lines TXDC/RXDC are located as alternate functions on
the port 4 lines P4.6 and P4.7. These two port lines have the standard port structure which is equal
to port 1 or port 3.
Semiconductor Group
6-16
1997-11-01