Specifications

HART ♦ ProLinx Gateway Functional Overview
HART Master Driver Manual
Page 12 of 119 ProSoft Technology, Inc.
July 7, 2009
Port Label Function
Channel 6 Hart Port 5
Channel 7 Hart Port 6
Channel 8 HART Port 7
The HART protocol uses the Bell 202 standard frequency shift keying (FSK)
signal to communicate at 1200 baud, superimposed at a low level on the 4 to 20
mA analog measurement signal. Having an average value of zero, an FSK signal
causes no interference with the analog value. The HART devices are powered
from this 4 to 20 mA analog loop.
All HART protocol channels in the ProLinx module generate the Bell 202 FSK
signal to communicate in multi-drop mode with up to 15 HART devices and
provide up to 300 mA supply for the analog loop in multi-drop mode. Refer to the
Reference chapter for ProLinx HART field connection information.
User configured commands determine the HART commands to be issued on
each channel to the HART devices. Up to 100 commands can be defined for
each port. Data read from the devices are placed in the virtual database. Any
write requests or device specific command for the HART slave devices are
sourced with data from the virtual database or from a configured constant data
block. In the commands it can be specified whether to use the HART device’s
short or long address. If the long address is selected, the device is polled first
with short address to ask for the long one. Then the device is polled with the long
address. The module does all this processing of the address automatically.
The module can be configured to place slave devices that are not responding to
commands from the master ports at a lower priority. If the module recognizes that
a slave device has failed to respond to a message after the user defined retry
count, it will mark the slave as "in communication failure" and set the error delay
time to the specified value. Each time that the error delay time expires, the slave
will be polled and if the answer is successful, the slave is placed again in an
active status. This facility can improve communication throughput on the HART
network.
In a HART network, it is possible to have two masters. The ProLinx module fully
supports the existence of a second master, but it can reduce the throughput on
the HART network. This facility is enabled or disabled in the module’s
configuration. If the ability to have a second master on the network is disabled,
then the maximum throughput is achieved.