RFDesign RFD868x - Page 14

Point-to-Point/SIK Firmware User Manual
www.rfdesign.com.au
15
Last update 17/12/2020
PPM
To enable PPM control signal pass through on a modem link it is necessary to set the ground station
modem to PPM input and the receiver modem to PPM output. This is enabled using the S registers
16 or 17. The PPM stream can then be injected/retrieved from GPIO1 (aka P1.1 or pin 15) the right
most pin on the bottom row of the header.
Input modem configuration AT commands:
ATPI=1
ATS16=1
AT&W
ATZ
Output modem configuration:
ATPO=1
ATS17=1
AT&W
ATZ
To record a failsafe PPM stream first connect the PPM generator to the ground station modem. Then
power up the receiving modem. Connect the ground station modem using the FTDI cable. After the
modems have established a link set the desired PPM failsafe stream using the generator and connect
to the ground station modem. Then send the following command to set the failsafe on the output
modem.
RT&R
RT&W
RTZ
This could alternatively be done by powering up the ground station and sending the PPM while
connected to the output modem via the FTDI cable in which case the command would be.
AT&R
AT&W
ATZ
Note: It is the the RC output modem that must record the failsafe mode.
Note: Different RC signal types can be inter-converted by the modem. e.g SBUS2_12CH input can be
output as SBUS2_18CH etc.