Rockwell Automation 1771-SPI,D17716.5.122 SPI PROTOCOL INTERFACE - Manual (Page 12)

Overview of an SPI Communication Network
Chapter 1
1-6
The SPI module can store the configuration blocks of:
up to 10 different types of devices (device types) such as mold
temperature controller, hot runner, and/or dryer controller
no more than one device (of a given device type) at a time
(for example, only one mold temperature controller)
unless they are identical with respect to:
- configuration, data, and status blocks
- command bits, such as for turning the device on or off
- presets, such as setpoints and alarm limits
- status bits and words
Exception : If you must network to different devices of the same type
(mold temperature controllers (MTCs) from different manufacturers),
then your program may become very complex because it must:
a. clear the previous configuration and data blocks
(for the MTC from company A)
b. replace them with a new set of configuration and data blocks
(for the MTC from company B)
c. communicate with the device from company B
d. repeat the three steps for each different device of the same type
(for the MTCs from companies C, D, etc.)
How Many Different Devices
Can the SPI Network
Handle?