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Chapter 5: Configuration
Table 5-2 (continued). S Register settings.
y < command
command name > x
Description
S217
Protocol Type
For most applications, the default value of 0—resulting in transparent
operation—will be maintained in this register. Setting this register to a value of 1
specifies MODBUS operation, in which the modem will frame the output data
and comply with MODBUS specifications. S217=2 configures the modem for DF1
filtering. In this mode, the PLC’s address must match the Unit Address of the
modem. Data not intended for a specific PLC/Modem pairing will be blocked
from passing through the modem to the attached PLC.
Values:
0 transparent
1 MODBUS RTU
2 DF1 protocol, full-duplex, with address filtering
S232
Maximum Buffer in
Storage
This register defines the maximum number of packets sent on the user serial
port that can be stored in the buffer.
Values:
1–255
200
S237
Sniff Timeout
This register applies only to Remote modems.
Defines how many hops the unit will sniff for when the Sleep Time (S144)
expires.
Calculate the Sniff Timeout (sniff duration) in milliseconds as follows:
Sniff Timeout=S237 (hops) x hop interval (per S109)
Values:
hops
1–255
10
Example: S237=20, S109=9 (=20 ms)
Sniff Timeout = 20 (hops) x 20ms per hop = 400 ms
NOTE: The longer the Sniff Timeout (duration), the likely the Remote modem will
“find” an upstream unit when you want to wake up the system; however,
more power will be consumed.
S244
Channel Request Mode Channel Request Mode “on” (default), allows a Remote modem that has data to
send to request permission from the Master. When granted, the Remote will be
allowed to transmit all of its data (no other Remotes may transmit during this
period), then it will release the channel. This feature eliminates collisions that
would otherwise occur if a number of Remotes were all trying to transmit at the
same time.
TDMA mode is discussed in detail in Section 5.2.1. In TDMA mode, the Master
does not allow Channel Requests from Remotes; the Master sequences through
a list of Remotes, giving each one in turn an opportunity to transmit.
Values:
0 Channel Request
1 TDMA Mode (Standard)
2 Fast TDMA
3 GPS Indexed TDMA
4 Adaptive TDMA
