Setup guide

Chapter 3 Driver and Protocol Objects
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Automationdirect.com 3-63 Object Reference Manual
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You can use the OffHook data member to enhance communications when
using the Modbus object class with dial-up modems. When OffHook is TRUE and the
serial port is connected to a dial-up modem, the Modbus object does not hang up the
modem when the poll is complete. Rather, it keeps the phone off the hook, retaining
exclusive use of the serial port. As long as OffHook is TRUE, the Modbus object
continues to poll the same PLC without hanging up the modem.
As soon as OffHook goes FALSE, the object releases the serial port to the
communications subsystem, which goes to the next poll request in the
queue, if any. The object also releases the port if data communications are
lost for any reason—such as if the PLC modem breaks the connection.
PollRate numeric no yes LookoutDirect
expression that
determines the device polling
frequency.
ProtocolErrors numeric yes no Total number of bad messages
received from polled device
ResetCounts logical no yes Resets number to zero in the
following data members: ValidFrame,
NoResponse, TooShort, BadCRC,
Garbled, Exceptions, &
ProtocolErrors
S400001 – S465000 numeric yes yes 6-digit addresses of 16-bit holding
registers encoded as signed binary
integers ranging from –32767 to
+32768.
S40001 – S49999 numeric yes yes 16-bit holding registers encoded as
signed binary integers ranging from
–32767 to +32768.
TooShort numeric yes no Number of responses from device
whose message length was too short
Update logical yes no Driver-generated signal that pulses
each time the driver polls the device
Val idF ra me numeric yes no Number of good messages received
from polled device
Table 3-12. Modbus Data Members (Continued)
Data Member Type Read Write Description