C515A_9708 Datasheet, PDF (55/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515A
The output drivers of port 1 to 5 have internal pullup FET’s (see figure 6-2). Each I/O line can be
used independently as an input or output. To be used as an input, the port bit stored in the bit latch
must contain a one (1) (that means for figure 6-2: Q=0), which turns off the output driver FET n1.
Then, for ports 1 to 5 the pin is pulled high by the internal pullups, but can be pulled low by an
external source. When externally pulled low the port pins source current (I_IL or I_TL). For this reason
these ports are called "quasi-bidirectional".
Read
Latch
Int. Bus
Write
to
Latch
Q
D
Bit
Latch
Q
CLK
V_CC
Internal
Pull Up
Arrangement
Pin
n1
Read
Pin
Figure 6-2
Basic Output Driver Circuit of Ports 1 to 5
MCS01823
Semiconductor Group
6-4
1997-08-01