Spi Communication Between The Isa100 Radio And The Sensor Board; Spi Configuration - Honeywell ISA100 Gen X User Manual

Radio module

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5. SPI Communication between the ISA100 Radio and the

SPI Inter-processor Communications (SPI_IPC)

The inter-processor interface between the Radio and the Sensor board is designed in such a way

that the Radio board can treat the Sensor board as a peripheral device. The Radio is the SPI

master and the Sensor board is the SPI slave. The SPI interface is not a query poll, but a bi-

directional pipe that supports messaging between the application layers.

Data Rate

The baud rate of the SPI UART controls the data rate. The baud rate selected is arbitrary, as the

SPI is a synchronous interface. For low power operation, the Radio SPI driver uses the 32768 Hz

ACLK to generate the SPI clock; a divide by 2 is the minimum (fastest) clock rate that can be

selected based upon the description in the MSP430 manual. This gives a bit rate of a baud rate of

15.384k baud. This provides a byte data rate of 2048 per second. This rate assures that there is

adequate time for the Sensor to process the SPI interrupts and maintain a reasonable packet

throughput. An ISA packet of 42 bytes takes about 20 msec transfer. MSP430 ACLK is used so

that the Radio and the Sensor can remain in the Low Power mode during data transfer as much as

possible.

SPI Mode

The sensor operates in the SPI Mode with – CKPL = 0, CKPH = 1 (normally low clock, data

clocked out on falling edge and clocked in on rising edge) using a four wire interface.

Arbitration

The Radio board is the SPI master and controls the transfer of data. The SPI interface is

designed to be in low power so that it does not require periodic polling, a physical layer data,

or headers to control the data transfer.

When the Radio needs to send data to the Sensor board (as in a request to a sensor block

received from the wireless network), it initiates the transfer spontaneously, provided the SPI

link is not currently in use. Packets can pass on the SPI link in both directions at the same time.

Each packet is treated as an individual, that is, as an independent message that is passed to the

appropriate application layer. An ISA100 packet transferred over the SPI is directed to the

ISA100 application layer to be parsed and transferred to a local object or routed to a network or

IR port.

Sensor Board

ISA100 Gen X Radio Module User's Guide

Honeywell

Release Independent

April 2018

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