Polling HART Devices - Fill Modbus Registers
To enable Modbus register accumula on, check the
Fill Modbus Registers
op on. The Hart Protocol Se ngs window will
expand to show the Polled Devices se ngs.
Retries
If a HART devices is polled but does not respond, or errors are detected, MicroLink-HM can retry up to 3 mes before
indica ng a bad device. If a device is not responding the Modbus values are
fi
lled with Hart Device Failed register
values - setup is done in the Modbus con
fi
gura on sec on.
Polled Devices
In the example screen shot (Figure 5), MicroLink-HM is set to poll one HART device using polling address 0 and will retry
1 me before repor ng a communica ons error. The
Device Variables (Modbus Register Values)
box on the right displays
the register values for the ac ve polled device. Click
Add Device
to add a polled HART device. Be sure to set the
Polling
Address
for each device. Each device must have a unique HART polling address. Polling addresses must be setup for
each HART device
before it can be
connected to a
mul -drop HART
loop and can be set
from 1 to 63.
Address 0 can only
be used when one
device is in the
HART loop.
Polling addresses
16-63 should only
be used with HART
revisions 6 and
higher. For HART
3-5 use addresses
1-15 for multi-drop
systems.
HART Protocol Settings
With
Fill Modbus Registers
unchecked, MicroLink-HM will func on as a standard HART protocol modem and not poll
HART devices to
fi
ll Modbus registers. In this mode HART packets are received and then retransmi ed at the HART
1200 baud, odd parity. Received reply packets are retransmi ed at
the selected baud rate. RTS ming and carrier detect are handled
internally by the MicroLink-HM allowing RS-232 communica ons at
higher than 1200 baud. HART loop data is handled at the standard
HART protocol 1200 baud, odd parity but because MicroLink-HM
bu
ff
ers the data the RS-232 port can be set for higher rates as well
as odd, even, or no parity. Port se ngs can be set in the Modbus
Se ngs sec on.
Since MicroLink-HM manages network timing it needs to be con-
fi
gured for either a primary or secondary master. Portable con
fi
gu-
ration modems are typically set to be secondary masters.
Figure 5. HART protocol se ngs dialog when
fi
lling modbus registers is enabled.
