Spectrum Controls 1756sc-OF8H Series A - Manual (Page 110)

96 ControlLogix ™ Analog HART Modules
Figure 7.18 (Long Frame Address)
Note: The IF8H and OF8H do not support burst mode.
The 1 byte Device Type code is allocated and controlled by the
manufacturer. The 3 byte Device Identifier is similar to a serial number in
that each device manufactured with the same Device Type Code must
have a different Device Identifier. The IF8H and OF8H automatically pull
for the device specific codes using the Auto-acquisition process. The
device specific codes that are acquired using this process can be seen in
Table 2.
Command
The command byte contains an integer (0 to hex FF or decimal 255) that
represents one of the HART commands. Code 254 is defined as an
expansion code and is followed by another byte allowing more than 256
different commands to be defined if necessary. The received command
code is echoed back by the slave device in its reply.
There are three categories of commands: universal commands, which all
HART devices must implement; common practice commands, which
should be used if the particular function is provided; and device specific
commands, which are for functions more or less unique to a particular
slave device.
Byte Count
The byte count portion of the message contains an integer value
representing the number of bytes that form the remainder of this message
excluding the checksum. In other words, the byte count determines the
length of the data and status.