User’s Manual
6-9
05.99
On-Chip Peripheral Components
C513AO
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 6-1.
Figure 6-7 shows a functional diagram of a port latch with alternate function. To pass the alternate
function to the output pin and vice versa, the gate between the latch and the driver circuit must be
open. Thus, to use the alternate input or output functions, the corresponding bit latch in the port SFR
must contain a “1”; otherwise the pull-down FET is on and the port pin is stuck at “0”. After reset, all
port latches contain “1”s.
Figure 6-8
Ports 1 and 3
Different structures apply for port pins P1.2 to P1.5, see Figure 6-9 and Figure 6-10.
MCS01827
D
CLK
Bit
Latch
Q
Q
Internal
Pull Up
Arrangement
Pin
Read
Latch
to
Latch
Read
Pin
Write
V
DD
Int. Bus
Alternate
Output
Function
Alternate
Input
Function
&