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Browse Prior Art Database

GRAY CODE SPI ADDRESSING TECHNIQUE

IP.com Disclosure Number: IPCOM000008643D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jul-01
Document File: 3 page(s) / 111K

Publishing Venue

Motorola

Related People

Tracy Plansky: AUTHOR

Abstract

This publication introduces a new method of selecting distinct SPI (Serial Peripheral Interface) devices in a given system in which the existing architecture is limited to a predetined number of address bits used for SPI device selection.

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MOTOROLA Technical Developments

GRAY CODE SPI ADDRESSING TECHNIQUE

by Tracy Plansky

INTRODUCTION

  This publication introduces a new method of selecting distinct SPI (Serial Peripheral Interface) devices in a given system in which the existing architecture is limited to a predetined number of address bits used for SPI device selection.

BACKROUND

  Several Land Mobile Base Radios utilize a particular SPI architecture in which multiple devices communicate with a Host device via a

common SPI bus. Each of the devices is individually selected by the decoding of address bits. Due to the absence of a global Chip Enable signal, inadvertent chip selection may occur due to the occurrence of simultaneous address bit switching. This inadvertent device selection is due to the various propagation delays within the system as well as the switching thresholds within the address decoding logic. As the system increases in size and signal filtering becomes necessary, the rise and fall times of the address bits become slower resulting in more noticeable inadvertant chip selections. Refer to Figure I.

single Seq 1 .OOCS/

182ns -117ns

: Ott 1996 1:57:29

Fig. 1 Channel 1: lnadvertant Chip Select

Channels 3,4,5,6,8: Address bits (plot by: Paul Harris)

176 March 1998

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MO7VROLA Technical Developments

  Notice that Channel S1 signal has a fall time that is much slower than Channel 6. The duration of this fall time allows Channel 6 to reach its Logic "0" threshold sooner than Channel 8, producing an inadvertant chip select.

SOLUTION

  Initially, a list of all the valid SPI device address values must be generated. Secondly, a list of all unused SPI device address values must be generated. The object of the GRAY Code SPI Addressing Technique is to toggle one address bit at a time allowing that value to stabilize then toggle another address bit, etc. It is important however, that only a...