C509-L_97 Datasheet, PDF (92/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6.1.2 Alternate Functions
Several pins of ports 1, 3, 4, 5 and 6 are multifunctional. They are port pins and also serve to
implement special features as listed in table 6-1.
Figure 6-11 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 1.4 and ports 5.0 to 5.7 when operating in compare output mode).
After reset all port latches contain ones (1).
Read
Latch
Alternate
Output
Function
V_CC
Internal
Pull Up
Arrangement
Pin
Int. Bus
Write
to
Latch
Q
D
&
Bit
Latch
Q
CLK
Read
Pin
Alternate
Input
Function
MCS01827
Figure 6-11
Circuitry of Ports 1, 3, 4, 5 and 6.0 through 6.2
Ports 6.3 through 6.7 have no alternate functions as described above. Therefore, the port circuitry
can do without the switching capability between alternate function and normal I/O operation. This
more simple circuitry is shown as basic port structure in figure 6-3.
Table 6-1 :
Alternate Functions of Port Pins
Port
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
Pin
INT3/CC0
INT4/CC1
INT5/CC2
INT6/CC3
INT2/CC4
T2EX
CLKOUT
T2
Alternate Function
External interrupt 3/capture 0/compare 0
External interrupt 4/capture 1/compare 1
External interrupt 5/capture 2/compare 2
External interrupt 6/capture 3/compare 3
External interrupt 2/capture 4/compare 4
Timer 2 ext. reload trigger input
System clock output
Timer 2 external count input
Semiconductor Group
6-14
1997-10-01