Microcontroller Basics Course (2)
port characteristics and port accesses
In the first instalment of this basics course, we introduced the assembler that we will be using. Now we come to the first practical applications using the processor ports. First, though, we have to take a look at the physical characteristics of the port connections.Anyone who already has a bit of experience with digital electronics knows that there are many different types of outputs. Each type has quite specific characteristics, regardless of whether it is a TTL, CMOS, tri-state, opencollector or open-drain output, and if you want to connect something to the output you need to be aware of these characteristics.In any case, the Port 1 outputs of an 8051 microcontroller do not fall in line with any of the know logic families, but instead employ a rather unique solution. These ports are what is known as ‘quasi-bidirectional’, which means that they can be used as inputs or outputs without having to be specially switched over.
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