805U Radio Modem Module
User Manual
Page
40
©
November 2004
via repeaters 2 and 3. Up to 5 repeater addresses may be used. A repeater can already be
connected to another module - it can still act as a repeater for another link.
Once a connection is made (DCD set), any data sent will be acknowledged by the other
module. The connection will be broken (DCD reset) if an ACK is not received within 5
attempts to transmit a message.
Either host may disconnect the link using the ATH command - or by using the DTR signal
on the RS232 port - refer to the AT&D command in Appendix A.
When the link is disconnected for any reason, the DCD output at each module is reset and
each module will respond to its host with NO CARRIER - each module will revert to
command mode.
Fast Operation Mode
Not used.
Controlled Mode Link Check and Reset times
If the master module has not sent or received a radio message within a preset time, it will
send a check message to make sure that the link is still active. If it does not receive a
response from the slave unit, it will disconnect the link and reset DCD. The check time can
be configured using the ATS6 command. For example, ATS6=10 sets the check time to 10
sec.
If the slave module does not receive a radio message within the link reset time, it will
disconnect the link and reset its DCD. The link reset time can be configured using the AT\T
command. For example, AT\T12 sets the link reset time to 12 seconds. The link reset time
should be larger than the link check time.
Note that any module can be master or slave - the master module for a specific link is the
module which initiated the connection (by ATD).
The default for both of these parameters is 0 which disables the link check and link reset
function.
Configuration of Flow Control
CTS/RTS flow control can be configured. This may be desirable to ensure data is not lost if
transmitting large amounts of data.
AT&K
&K0
Flow Control Disabled. CTS Always high. Module ignores host’s RTS. Select
for full duplex RS232 with no flow control.
&K1
not used
&K2
not used
&K3
CTS/RTS Flow Control. CTS Reflects the state of the local buffer. Module
only transmits serial data when RTS is high.
&K4
(default) RS-485 Control - flow control disabled. Must be selected for RS-485
to work. CTS is high. CTS goes low when transmitting data. RTS is ignored.
