C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 83

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

6.1.1.2
6.1.1.2.1 Basic Port Circuitry of Port 1 to 6 and 9
The basic quasi-bidirectional port structure as shown in the upper part of the schematics of
figure 6-1 provides a port driver circuit which is build up by an internal pullup FET as shown in
figure 6-3. 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 6-3: Q=0), which
turns off the output driver FET n1. Then, for ports 1 to 6 and 9, 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 (
Figure 6-3
Basic Output Driver Circuit of Ports 1 to 6 and 9
Semiconductor Group
Quasi-Bidirectional Port Structure
I
IL
or
I
TL
Int. Bus
). For this reason these ports are sometimes called “quasi-bidirectional”.
Latch
Latch
Read
Read
Write
to
Pin
D
CLK
Bit
Latch
6-5
Q
Q
On-Chip Peripheral Components
MCS01823
V
CC
n1
Internal
Pull Up
Arrangement
Pin
1997-10-01
C509-L