Memory and Input/Output Interfacing
- Interfacing is the process of connecting memory and input/ouput devices with a microprocessor or computer.
- Fig shows the use of decoders to connect microprocessor-8085 with memory input/ output devices.
- Some of the address lines of 8085 microprocessor are connected to decoder 1 and decoder 2 shown in figure below to select either a memory chip or an input/output device.
- When pin IO/M=Low(0), decoder(1) is enabled and the required memory chip is selected when pin IO/M = High(2) is enabled and required input/Output is selected.
The process of connecting a memory device with a microprocessor or computer is called interfacing and the devices used for connecting memory with a microprocessor or computer are interfacing devices.
The address of a memory location or an input/output device is sent out by microprocessor and corresponding memory or an input/output device is selected by the decoder circuit.
In the figure below decoder 7415138 decoder and it is a 3X8 decoder i.e. it has 3 input lines and corresponding 8-output lines G1, G2A and G2B are the enable signal of the decoder. i.e. to enable decoder its must that G1 should be high and G2A and G2B should be low.
A, B,C are the enable lines and by applying appropriate signal at these lines any of the 8 output lines O0—O7 can be selected.
An output lines goes low when it is selected while other output lines remain high at this time.
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