Browse Prior Art Database

Dual Function I/O Port

IP.com Disclosure Number: IPCOM000044836D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Smith, BA: AUTHOR

Abstract

By using one input/output (I/O) port for two functions, other I/O ports may be freed up for other uses. An input port is used at the beginning of a program to determine in what operating mode the code should be. At a later time, the same port may be used as an output to indicate successful task completion. The input signal is buffered by an open collector device and the signal's polarity is chosen such that the buffer output will be high when the microcomputer uses the I/O port for an output. Since the buffer's output transistor is off, the I/O port can be toggled as desired. This can help to conserve the I/O ports in a design and minimize additional parts.

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Dual Function I/O Port

By using one input/output (I/O) port for two functions, other I/O ports may be freed up for other uses. An input port is used at the beginning of a program to determine in what operating mode the code should be. At a later time, the same port may be used as an output to indicate successful task completion. The input signal is buffered by an open collector device and the signal's polarity is chosen such that the buffer output will be high when the microcomputer uses the I/O port for an output. Since the buffer's output transistor is off, the I/O port can be toggled as desired. This can help to conserve the I/O ports in a design and minimize additional parts.

Referring to the Figure, an example will be given. A -WRAP line indicates the off-line mode. This signal is applied through inverter 10, such as a 74 O6, having an open collector output. The output of inverter 10 is coupled over a line 12 to an I/O port 14. Line 12 is coupled through a pull-up resistor 16 to a source +V voltage. Line 12 is also coupled to a -GOOD signal from the processor which goes to ground level after successful completion of the diagnostics. Thus, the single port I/O 14 is being utilized by two signals.

Disclosed anonymously

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