Westermo RM-455U-D - Manual (Page 41)

455U-D Radio Modem User Manual
Page 42 © May 2010
DCD Control
The DCD signal on the RS232 port can be used to give an indication of communications link
status in Acknowledged mode. Note that the link is always connected in unacknowledged
mode.
 “Always On” - the 455U-D sets the DCD to be always on
 “Only High When Connected” - the DCD signal will be on when the link is connected and
off when the link is reset
 “Pulse Low on Disconnect” - the DCD signal will be normally on but will switch off
momentarily (for 0.5 sec) when the link is reset.
Packet Size (bytes)
This selects the maximum number of bytes which will be transmitted in one message. If more
than this number of bytes is input into the 455U-D, then the module will transmit more than
one message.
The default value is 1020 bytes which is the largest packet value. If you are operating in a
noisy radio environment, then the system may be more reliable if you reduce the maximum
packet size and transmit a larger number of small messages rather than a lesser number of
large messages.
Packet size is configured via S-Register S14. The value in S14 is multiplied by four to get the
maximum packet size.
Transmit and Receive Hold-off delay times
A “transmit delay” time and a “receive delay” time can be configured. These parameters may be
used to fine tune and give priority to different 455U-D units in a system.
 Transmit delay - S16. After each message is transmitted, a 455U-D unit will not transmit
another message during the transmit delay time. This could be used to allow a reply message
to be received before the next message is sent.
 Delay time - S17. After a message is received, a message will not be transmitted during the
receive delay time. This could be used to delay a reply message until other messages have
been sent.
3.7 Acknowledged Mode
Refer to section 1.3. There are several configurations for Acknowledged mode:
3.7.1 Auto Dial (Auto-Connect Master)
Auto-connect mode is similar to “fixed line” modem operation. The master unit wants to
connect to only one slave address. Normally the slave address is preconfigured. On power
up, the master unit continuously tries to connect to the slave address. The slave unit, on
power up, does not try to connect but waits for a connect message. Once a connection is
made, the DCD status at both ends is set and data can be transferred in either direction.