Rockwell Automation 1771-SPI,D17716.5.122 SPI PROTOCOL INTERFACE - Manual (Page 7)

Chapter
1
1-1
Overview of an SPI
Communication Network
This overview chapter contains:
purpose of the SPI network
types of data communicated on the SPI network
role of the SPI module
role of the host PLC-5 processor
what you program
how the SPI module polls its network devices
The protocol developed by the Society of Plastics Industry provides a
standard for transferring command and status data between a master interface
(SPI module) and slave devices on a network. This provides for compatible
network communication among devices made by various manufacturers.
Typically, a master interface can use SPI protocol to communicate with
slave devices on the network to:
send them command data such as
- bit-level commands
- setpoints
- high/low deviation alarm limits
receive from them status data such as:
- bit-level indicators of detected alarm conditions
- current operating parameters (process actuals)
The SPI module is the network master that coordinates the flow of data
between the PLC-5 host processor and slave devices on the network.
The SPI module:
stores configuration information corresponding to each device
returns configuration status to the host PLC-5 processor
receives command data destined for devices on the network
temporarily stores the data while it polls the target device
sends data serially to and receives status serially from the target device
repeats the data transfer for each device in polled order
returns status data from network devices to the host PLC-5 processor
What This Chapter Contains
Purpose of the SPI Network
Types of Data
Communicated
on the SPI Network
Role of the SPI Module