User`s guide

number of attempts an ACK message is still not received the link connection is
effectively terminated and the data packet is discarded.
The default setting for the number of data packet retry attempts is usually adequate for
most situations. However if the radio modems are being used in an RF noisy
environment or an environment prone to short signal interruptions (trucks passing
between the link, etc) thus resulting in lost data, then the number of packet retry
attempts should be increased slightly. Note however that the retry attempts are no fix
for a poor signal RF path.
Acknowledged Point to Multipoint
This mode of operation is, in principal, identical to the point-to-point mode. Hence,
connection setup, data transfer, data acknowledgements and disconnection all work in
the same manner. What makes this mode specific to point-to-multipoint operation is in
the configuration of the slave devices and the use of the addr command to
dynamically change the unit address, site code and optionally the hop count.
Please refer to the paragraph on Acknowledged Point-to-Point mode for a description
of link connection, data transfer and acknowledgements.
When using the RMX232 in a point-to-multipoint configuration, one modem is
designated as the master unit while all other modems are assigned the status of a
slave and given a different unit address and site code, and possibly hop count if a
repeater is required to access a distant slave modem.
The master modem is configured with ptpmode set to ON (as in point-to-point mode).
In order for the modem to address a slave modem, the connected host device must
enter the configurator using the +++ sequence, then issue the addr command with
appropriate parameters, followed by a carriage return. A period symbol (“.”) is
returned as confirmation that the parameters have been assigned to the appropriate
RAM based unit address, site code and/or hop count. The modem is then ready for
connection and transfer of data to the addressed slave modem.
A slave modem is configured with the ptpmode set to slave. Setting ptpmode to slave
effectively disables the radio modem from establishing a connection with the master.
Hence the master modem is required to establish a connection with a remote modem,
before data stored in a slave serial buffer can be sent.
The basic operation of a system using the RMX232 in point-to-multipoint mode can be
described with the following PROCOMM 4 script that would be run on the host
controller connected to the master modem. Lets assume, the slave modems are
connected to a device which responds with data to a message from the master.
; PROCOMM 4 Aspect Script. Point-to-Multipoint demonstration (Master code)
proc main
while 1
pause 1 ; Wait before sending ‘+++’
transmit "+++" ; Enter configurator
waitfor ">" 1 ; Confirms entry to configurator
transmit "addr 0^M" ; Set the address to 0
waitfor "." 1 ; Confirms setting has been accepted
transmit "<somedata>" ; Send data to unit 0
; Wait here for a response if required
pause 1 ; Wait before sending ‘+++’
transmit "+++" ; Enter configurator
waitfor ">" 1 ; Confirms entry to configurator
transmit "addr 1^M" ; Set the address to 1
waitfor "." 1 ; Confirms setting has been accepted
transmit "<somedata>" ; Send data to unit 1
; Wait here for a response if required
endwhile
endproc
User’s Guide Modem Operation Explained 4-7