Page 125 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 8: Interfacing I/O Devices

8.3.11 Interfacing the Switches Notes

• The binary value from the switches will have to be carried by the data bus. However, the data
bus is a shared bus. So, the switches must be connected to the data bus using Tri-state buffers.

• Similar to the latch, the buffers must be enabled only on I/O Read operation from this I/O
port.
• Lets choose I/O port 0FH for the switches. So, the buffers must be enabled when:

– RD = 0
– IO/M = 1

A8-A15 = 0FH
8.3.12 Interfacing the Switches (Control Circuit)

Figure 8.3: Interfacing the Switches (Control Circuit)

8.3.13 Interfacing the Switches (Latch & Switches)

Figure 8.4: Interfacing the Switches (Latch & Switches)

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