MILACRON MFC-G - SPI Commands

Temperature Control Units : MFC with G Series Instrument
Page: 84
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8.5 SPI COMMANDS
A. INTRODUCTION: In 1987 a group of member companies of the Society of the Plastics
Industries began development of a communication protocol for use by their processing
and auxiliary equipment. Their goal was to allow the exchange of information between
various pieces of equipment from different manufacturers to be simple and reliable. The
result of their work was released in 1990 and has made the interconnection of equipment
much easier and straightforward. There are now over 40 companies that offer the SPI
Protocol in their products. This document details the implementation of the SPI Protocol
available in the temperature controllers and portable chillers with HE instruments.
B. PROTOCOL BASICS: The SPI Protocol is described by a 2 part specication. The
largest portion of the SPI Protocol specication deals with how basic information is
exchanged between equipment. The second part of the specication details the actual
pieces of information exchanged using the protocol. Items such as Process Temperature,
Process Setpoint and Process Status are detailed in this part. This FYI will list the
commands that are supported by this equipment.
C. EQUIPMENT SETUP: The setup of equipment to be connected in an SPI Protocol
network is simple. Each device must have a unique address for its device type and it
must use the same data transfer rate as the other pieces of equipment in the network.
There are many acceptable ways used to ‘set’ the device address and data rate.
Equipment provides access to the information via the front panel operators and displays.
Other manufacturers may use internal DIP switches or jumpers.
A typical cell may be congured as follows:
Data Transfer Rate: 9600 bits per second (bps)
Mold Temperature Controller (Qty 2): Addresses 1 and 2
Chiller (Qty 1): Address 1
Note in the above example that different device types may have the same address. This
is because the SPI Protocol uses the device type as part of its internal address.
D. NETWORK TROUBLESHOOTING: Troubleshooting a network is best done by verifying
the setup of each piece of equipment and insuring that the network is installed with the
correct electrical interconnection. Here are some basic things to do if equipment isn’t
‘talking’ as expected.
1. Verify that each piece of equipment is properly grounded to its power source.
2. Inspect cables inside and outside the electrical cabinet. Repair or replace
as necessary. The cable scheme used by most manufacturers allows the
communication signals to ‘pass through’ each piece of equipment. Therefore,
when a piece of equipment is disconnected from the middle of the network, all
the equipment ‘after’ that one will be disconnected, too. If a piece of equipment
is being permanently removed, the device cables should be rearranged at the
molding machine to reconnect the other equipment.
3. Check the Data Transfer Rate and Address of each piece of equipment. For