C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 66

• Manufacturer Part Number: C505_9708
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

The output drivers of Port 1 to 4 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 4 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 (
these ports are called "quasi-bidirectional".
Figure 6-2
Basic Output Driver Circuit of Ports 1 to 4
Semiconductor Group
Int. Bus
Read
Latch
Latch
Read
Write
to
Pin
D
CLK
Bit
Latch
6-4
On-Chip Peripheral Components
Q
Q
MCS01823
V
CC
n1
Internal
Pull Up
Arrangement
Pin
I
IL
or
I
TL
C505 / C505C
). For this reason
1997-08-01