Browse Prior Art Database

DUAL MODE TOGGLE LINE

IP.com Disclosure Number: IPCOM000008999D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-30
Document File: 4 page(s) / 151K

Publishing Venue

Motorola

Related People

J├╝rgen Schmidt: AUTHOR [+3]

Abstract

This idea deals with optimized Master/Slave communication on SPI (Serial peripheral interface) devices in embedded microprocessor controlled sys- tems.

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MOTOROLA Technical Developments

@

DUAL MODE TOGGLE LINE

by Jiirgen Schmidt, Horst Geib and Graeme Johnson

ABSTRACT

  This idea deals with optimized Master/Slave communication on SPI (Serial peripheral interface) devices in embedded microprocessor controlled sys- tems.

INTRODUCTION

  A problem in current SPI systems is the use of complex SPI devices without a protocol based com- munication. For example a "dump" A/D converter must be told via the SPI interface to start a conver- sion. In this case it is common for a microprocessor to take the role of the SPI master, and the AD con- verter to take the slave role. The Master has to poll the status of the conversion process via an additional line. When conversion is finished then the Master initiates a read of the data via the SPI interface. This is an example for a simple fixed length data package communication. Devices which use a pro- tocol on the SPI bus rnn into more difftculties.

PROBLEM(S) ~0 BE HALVED

  There is a need to #signal the beginning and length of a data package: This is the problem e.g. in a control head of a two-way radio. Such a conligu- ration needs to transfer !,variable length data pack- ages in both directions: 'from radio to control head
e.g. display information; from control head to radio
e.g. key strokes.

Common solutions are:

  a) Use a separate line for signaling data transfer in both directions. This solution results in addition- al costs for the hardware connection; especially when the radio and control head are separated, e.g. via a 7 meter "remote" cable.

  b) Determine Master/Slave ownership for every transfer separately. This solution requires a protocol overhead and an intelligent SPI device at both ends of the SPI bus.

0 MOtmOl?. Inc. 1999 140 January 1999

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MO7WROl.A Technical Developments

PROPOSED SOLUTION TO THE PROBLEM(S)

This idea uses only one line for both signalling directions and leaves the Master ownership always at the same device. The configuration looks like the following schematic:

Request Select

MOSI = Master data out, Slave data in MIS0 = Master data in, Slave data out

Fig. 1 Configuration schematic

In the description on the next page, the signaling line is called "request". The meaning of the request line changes during a data package transfer from "request" mode to a "handshake" mode. The details are explained in the example transfer diagram on the next page, assuming the radio is Master and control head is Slave.

0 Motorola. Inc. 1999 141 January 1999

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MOTOROLA Technical Developments

1 6 10 14 17 20 22

request I I I I

Slave select

MOSI

I

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opcode no of bvtes data

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MIS0

CSR = Check sum radio CSH = Check sum (control) head

Fig. 2 SPI data transfer diagram

SPI data transfer diagram description (The numbers...