Spectrum Controls 1734sc-OE2CIH - Manual (Page 39)

Chapter 4: OE2CIH and HART 4-3
User’s Manual Pub. 0300272-01 Rev. A.0
has been refreshed by the module, and you should re-send the Read Additional Status
CIP message to the class instance (Instance=0) that returns all channels at once. (Sending
a request for an individual channel does not reset the tag.)
The data returned by the Read Additional Status is in the original order as received from
the HART device. This means any multi-byte elements in the data will not be in the
correct order for use in RSLogix, and will be reversed in the PLC. HART format is most-
significant bit (MSB) first, while RSLogix is least-significant bit (LSB) first for multi-
byte variables. The module is unable to re-order the bytes because it does not have
knowledge of where the multi-byte elements are within the data, and this can vary from
device to device. Refer to the HART device’s documentation for the location of each
multi-byte element, and reverse the order of the bytes in ladder to interpret.
4.2.3 Automatically Gathering HART Device Information
Upon first connection with a HART device, the module sends a series of HART
commands to retrieve information about that device. The module will store this
information so that it can be retrieved at any time (by the PLC) using a CIP unconnected
message.
Table 4-1 HART Initialization Sequence
Commands sent at Initial Device Connection
Command: Definition: Comment:
0 Read Unique Identifier Associated
with Tag Sent using Short Address to find device
6 Write Polling Address Only sent if device responded at non-zero
Addr
59 Write Number Of Response
Preambles Selects a minimum number of preambles to
be sent by a device before the start of a
response packet.
12 Read Message Reads the message contained within the
device.
13 Read Tag, Descriptor, Date Read the tag, descriptor, and date contained
within the device.
15 PV upper and lower range values Reads the Primary Variable Alarm Selection
Code, Primary Variable Transfer Function
Code, Primary Variable Range Values Units
Code, Primary Variable Upper Range Value,
Primary Variable Lower Range Value,
Primary Variable Damping Value, Write
Protect Code, and Private Label Distributor
Code associated with the device or the
Primary Variable.
16 Read Final Assembly Number Read the Final Assembly Number
associated with the device.
48 Read Additional Device Status Returns transmitter status information not
included in the response codes.
50 Read Dynamic Variable Assignments Responds with the Transmitter Variable
numbers that are assigned to the Primary,
Secondary, Tertiary, and Quaternary
Variables
3 or 9 Read Dynamic Variable Assignments Command 3 if HART rev 5; otherwise
Command 9 is used