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Command of Several Light Emitting Diodes with few Inputs/Outputs

IP.com Disclosure Number: IPCOM000118408D
Original Publication Date: 1997-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

In telecommunication equipment, we are often faced with the following problem: How to command a lot of independent Light Emitting Diodes (LEDs) with a minimum of Inputs/Outputs (I/Os) pins. The classical method is as follows (Fig. 1): (Image Omitted)

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Command of Several Light Emitting Diodes with few Inputs/Outputs

In telecommunication equipment, we are often faced with the following problem: How to command a lot of independent Light Emitting Diodes (LEDs) with a minimum of Inputs/Outputs (I/Os) pins. The classical method is as follows (Fig. 1):

(Image Omitted)

A register is written with a word of a length corresponding to the number of LEDs to command and a control lead is used to load the register. It is easily noticed that if the number of LEDs is growing up, the needed I/Os of the chip are growing proportionally. If the chip is a microprocessor or a microcontroller, we can use their data bus plus a decode, so this solution is correct, but if the chip is a gate array, an FPGA or an EPLD, each I/O is usable, and it is not reasonable to use an I/O per LED to be driven. Another method can be employed: The command information, issued from the chip, can be serialized into the chip and then sent out to the shift register (Fig. 2).

The output of each latch of the shift register can drive each LED. This method gives the possibility to drive a large amount of LEDs with only two I/Os. The update of the status of the LEDs can be performed at any time without any perception of blinking if the clock is fast enough (>1KHZ).

It is to be noticed that the clock is not a free running clock but a burst sent by the chip. The number of clock beats is equal to the number of LEDs to be commanded (Fig. 3).

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