Spectrum Controls 1769sc-HART Modules - Manual (Page 98)

Compact IO™ Isolated HART Analog Input Module
User's Manual 0300215-03 Rev. A
7-30
Section 7.4
Module Specific
Commands
The HART input module uses module specific commands. Module specific commands
include the HART pass-through, HART suspend and resume, and get HART device
information. The commands are passed to the module using the input and output image.
Since some messages can be as long as 257 bytes, the data is transported to and from the
module 40 bytes at a time using the paging scheme described in the previous section.
The module specific command and accompanying data is passed to the routine in Figure
7-8 using a JSR instruction with parameters. When the routine is executed it will send
the message to the module. The response data if any is also converted by this routine and
stored in a temporary array where it can be used within the ladder program. See figure
below.
Figure 7-9 (Message Flow)
The tables on the following pages show the format for each module specific command.
7.4.1 Get HART Device Information
The Get HART Device Information command is used to gather the device specific
information for the connected HART device. The data that is retrieved can be seen in
Table 7-11. The information that is gathered by this command is similar to the
information gathered from the auto-acquisition process. The key difference is that the
Get HART Device Information command pulls the data that has been stored in the module
RAM and not directly from the field device.
Table 7-9 (Get HART Device Information Command)
HART Get Device Information – command message packet structure
Get currently cached Device Information for a given channel.
Field
Value Definition
HART Channel
Number 0x00 – 0x03 (1 byte) Module input
channel number for
HART command
Command Number 0x03 (1 byte) The command
number to obtain
HART device
information
Input Par: Message Size
Input Par: Message Body (i.e. Device Specific Command)
Return Par: Message Done
Return Par: Message Response (i.e. Temp Array)
JSR
Routine
Fig 7.9