C508_01 Datasheet, PDF (70/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
On-Chip Peripheral Components
The output drivers of Port 1, 2, 3, and 5 have internal pull-up FETs (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). This means for Figure 6-2,
Q = 0, which turns off the output driver FET n1. Then, for Ports 1 to 5, except Port 4, the
pin is pulled high by the internal pull-ups, 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-bi-directional”.
Read
Latch
Int. Bus
Write
to
Latch
Read
Pin
D
Q
Bit
Latch
CLK
Q
V_DD
Internal
Pull Up
Arrangement
Port
Pin
n1
MCS04042
Figure 6-2 Basic Output Driver Circuit of Ports 1, 2, 3, and 5
User’s Manual
6-5
2001-05