Nor-Cal IQ+ Adaptive Pressure Controller - Manual (Page 20)

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IQ+ OP-LIT 9/08
7.2 - DeviceNet Communications
This section describes how to communicate with and control the controller using the DeviceNet port. DeviceNet has two basic message types: Explicit and I/O
How initialize the valve (not required on all valve types):
• Select the service code 32 (initialize service)
• Select class ID 30 (select the s-device supervisor object)
• Select instance ID 1
How to transition the controller to the executing state:
To be able to perform pressure or position control by means of explicit
messaging, the controller has to be transitioned to the device Executing state.
• Select the service code
6 (start service)
• Select class ID 30 (select the s-device supervisor object)
• Select instance ID 1
How to control valve position:
• Select the service code 10 (set attribute)
• Select class ID 2E (select the selection object)
• Select instance ID 1 (setpoint)
• Select attribute ID 0E (destination used) followed by the data 02 (position
control)
then
• Select the service code 10 (set attribute)
• Select class ID 2E (select the selection object)
• Select instance ID 1 (setpoint)
• Select attribute ID 0F (source data value) followed by the setpoint 00 40
• The device will move the valve to 50% of its stroke
• Select attribute ID 0F (source data value) followed by the
setpoint 00 00 The device will move the valve to 0% of its
stroke or closed
How to control pressure:
• Select the service code 10 (set attribute)
• Select class ID 2E (select the selection object)
• Select instance ID 1 (setpoint)
• Select attribute ID 0E (destination used) followed by 01 (pressure control)
then
• Select the service code 10 (set attribute)
• Select class ID 2E (select the selection object)
• Select instance ID 1 (setpoint)
• Select attribute ID 0F (source data value) followed by the setpoint 00 20
(pressure control)
• The device will try to control pressure at 25% of full scale of the selected
pressure source
• Select attribute ID 0F ( source data value) followed by the setpoint FF 7F
The device will try to control pressure at 100% of full scale of the selected
pressure source
How to read the valve limit switch:
• Select the service code 0E (get attribute)
• Select class ID 8 (select the discrete input point object)
• Select instance ID 1 (closed limit switch)
• Select attribute ID 3
• The device will respond with data bytes 01 meaning that
the close limit switch is activated and the valve is closed
• Select instance ID 2 (open limit switch)
• Select attribute ID 3
• The device will respond with data bytes 00 meaning that
the open limit switch is not activated and the valve is not opened
messaging
Explicit messaging:
Explicit messages are used to read or write an individual piece of information
in the device. They are mainly used for initial configuration. Explicit messages
include the path to locate the data of interest, this consists of the class ID,
attribute ID, and instance number. They also specify an action to be taken.
The table below lists some of the key information available through explicit
messaging. Please refer to Section 9 for the full device profile characteristic.
TAbLE 7.3 - DEvICENET ExPLICIT mESSAGING
claSS
Id
HEx
InStance
Id
HEx
attrIBute
Id
HEx
ServIce Id
HEx
varIaBle
name
1 1 1 0E (get) Vendor ID
1 1 6 0E (get) Serial Number
1 1 7 0E (get) Product Name
3 1 1 0E (get) 10 (set) MACID
3 1 2 0E (get) 10 (set) Baud Rate
31 1 6 0E (get)
Process input
(low range)
31 2 6 0E (get)
Process input
(high range)
31 3 6 0E (get) Valve position
2E 1 5 0E (get) 10 (set)
Pressure control
and position
control
2E 1 9 0E (get) 10 (set) Process setpoint
The most straightforward way of sending individual commands to the
controller is to use a node-commissioning software utility. These utilities
are part of the DeviceNet interface card package.
Explicit messaging connection examples:
•
Power up the device, the network LED will transition to flashing green
• Let the master open an explicit connection with the device
• The network LED will transition to solid green
Note that in DeviceNet communications, data to and from the device is always
encoded least significant byte first as specified in the data management sec-
tion of the DeviceNet protocol specification. For instance the value 12345678
hex is encoded as follow:
octet numBer 1st 2nd 3rd 4th
outPut data 78 56 34 12
How to get device identity information:
•
Select the service code 0E (get attribute)
• Select class ID 1 (select the identity object)
• Select instance ID 1 (there is only instance supported)
• Select attribute ID 1 (vendor ID attribute)
• The device will respond with data bytes 64 02 meaning 264 hex
or 612 dec, which is the vendor ID that has been attributed to
Nor-Cal Products Inc.
• Change the attribute ID for 6 (serial number attribute)
• The device will respond with data bytes on the form, 3A b1 02 00
meaning 2B13A hex or 176442 dec, which is the serial number of the
device.
(Nor-Cal device serial numbers are composed of at least 6 digits)
Note: The examples above assume that default data
type (INT) and data units (Counts) is used.