Siemens EF 88H Series Bedienungsanleitung PDF herunterladen (Seite 37)

Semiconductor Group 6-3

On-Chip Peripheral Components

C501

Port 1, 2 and 3 output drivers have internal pullup FET’s (see figure 6-5). 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 6-5: Q=0), which turns off the output driver FET n1. Then,

for ports 1, 2 and 3, 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 (

or I

). For this reason these

ports are sometimes called “quasi-bidirectional”.

Figure 6-5

Basic Output Driver Circuit of Ports 1, 2, and 3

MCS01823

CLK

Bit

Latch

Internal

Pull Up

Arrangement

Read

Latch

Read

Write

Int. Bus

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Siemens EF 88H Series Bedienungsanleitung Seite 37