User's Manual

12
Auto Link Operation
Setting and storing the modules Auto Link settings into the modules Non Volatile
Memory (NVRAM) allows the pre-configuring of the modules DTE speed, data link
speed, transmit levels, frequency of operation, and channel Ids for establishing a constant
wireless data link. Once these parameters are stored, the module will be conditioned to
automatically maintain a connection. In the event of a power outage, the modules will
automatically attempt to reconnect to each other when power is restored. If the wireless
data link is lost due to any other reasons, the modules will detect the lost link and attempt
to automatically re-establish the link forever.
To configure the modules for Auto Link operation using the modules in their default
state, one module must be set up for Answer Mode and the other must be set for Originate
Mode. Send the “ ATS0=1&W” command followed by a <CR> (carriage return or Enter
Key) to one module and Send the “ ATS0=2&W” command followed by a <CR>
(carriage return or Enter Key) to other module. Once these command strings are issued,
the modules are set up for Auto Link Operation. After a five second delay they will
attempt to automatically establish a wireless data link. During the link process the
originating module will display “LINKING-O” The answering module will display
“ LINKING-A”. If the link is successful, the WHM900 modules will each display the
appropriate “CONNECT” result codes. After the CONNECT result codes are displayed,
the modules will be in On Line Data Mode and data transmission is now possible. The
data link between the modules is always error corrected so data will be received exactly
as it was sent. If data appears to be missing, verify that the data flow control is the same
on the Host and WHM900. The WHM900 defaults to Hardware Flow Control
(RTS/CTS). See the AT\Qn command change the modules flow control settings. If data
throughput is slow, set the Host equipment interface speed the same or higher than the
modules connect speed. The maximum DTE or Host interface speed is 57.6kbps. The
module will automatically detect and adjust to the new DTE speed upon receipt of the
next “ AT” command the module receives.
If the ATS7 Register time expires and no data link was completed, the modules will
display the NO CARRIER result code and begin the link negotiation process again. This
process will continue indefinitely until a wireless data link is established. If a wireless
data link is interrupted, the modules will attempt to re-establish the connection. Each
attempt to re-connect will take approximately 10 seconds. The ATS18 Register
determines how many times the module will attempt to re-connect. The “ NO LINK”
result code will be displayed after each failed attempt. If unable to successfully connect,
the “ NO CARRIER” result code will be displayed. This routine will constantly repeat
until the modules re-establish a wireless data link.
Note: Always save the Auto Link options as well as any other command parameters with
the AT&W command. When the module is reset or powered up it will always revert to
these saved settings. The module will also power up to the DTE speed that the last
AT&W was issued.