XBee
‐
PRO®
900HP
RS
‐
232/RS
‐
485/USB
RF
Modem
‐
Product
Manual
©
2013
Digi
International
Inc.
14
2 .3 . RS- 4 8 5 ( 4 - w ir e ) Ope r a t ion a n d RS- 4 2 2 Ope r a t ion
Note that with the RS-485 variant of the 900HP RF Modem, the RF Modem is defaulted with the D7
command (AT parameter) to 7. This parameter controls the TX enable signal and allows the
modem to output any data in the DO buffer to the host device for the RS-485/422 interface. In the
event that the parameter is accidentally changed, which would halt RS-485 communication, a USB
mini cable should be plugged into the modem to reconfigure it. You can reconfigure by using Digi's
X-CTU.
With the USB plugged in:
1. Open X-CTU and select the Com port of the USB.
2. Select the Terminal tab and type “+++”. The system will respond with “OK”.
3. Type “ATD77” then <Enter>, and the system will respond with “OK”.
4. Type “ATWR” then <Enter>, and the system will respond with “OK”.
5. Type “ATCN” then <Enter> to exit command mode, and the system will respond with “OK”.
6. Unplug the USB and return to the existing RS-485/422 interface. The 900HP RF Modem is
now ready to communicate in RS-485 mode.
N OTE
: Failure to enter AT Command Mode is most commonly due to baud rate mismatch. Ensure
the 'Baud' setting on the “PC Settings” tab matches the BD (Interface Data Rate) setting of the RF
modem (by default, BD parameter = 3, which is associated with 9600 baud).