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ECE 447: Lecture 11

ECE 447: Lecture 11. Port Multiplexing. ECE 447: Port Multiplexing. Allow multiple devices to share the input and output ports of the microcontroller. Additional hardware typically needed to support connection and selection of peripheral devices.

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ECE 447: Lecture 11

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  1. ECE 447: Lecture 11 Port Multiplexing

  2. ECE 447: Port Multiplexing • Allow multiple devices to share the input and output ports of the microcontroller. • Additional hardware typically needed to support connection and selection of peripheral devices. • Software typically selects the peripheral devices using additional output pins. • Some I/O devices have built-in enable signals.

  3. ECE 447: Octal Buffer 74LS245 Note: All 8 outputs controlled by one enable, OE

  4. ECE 447: Octal Buffer 74LS244 Note: Outputs controlled by two enables, 1G & 2G (1G controls 1A1-1A4, 2G controls 2A1-2A4)

  5. OE ECE 447: Port Multiplexing MC68HC11 Port C Port B 8 1G 2G 74LS245 74LS244 DIR I/O device 2 (e.g., keypad) I/O device 1 (e.g., LCD display)

  6. OE OE 74LS245 74LS245 DIR DIR ECE 447: Port Multiplexing MC68HC11 Port C Port B . . . . . . . . . . . . I/O device 1 I/O device 8 . . . . . . .

  7. OE ECE 447: Port Multiplexing A/D? MC68HC11 Port E MAX4781 74LS245 DIR Analog Device Digital Device Input device 1 Input device 8 . . . . . . .

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