Geofrancis wrote:you are correct in that it would stop operation with sport xjt, i use a modified djt with ttl mod so that i can swap between openlrs and frsky telemetry by just changing modules since both are on ttl levels.
The 9XR-PRO was designed to support both inverted RS2323 levels and inverted or non-inverted ttl levels on the bottom pin of the module connector for receiving telemetry. The signal input tolerates RS232 levels as well as ttl levels and includes a firmware controlled hardware inverter to select the required sense. As such, a DJT may be used just by wiring the Tx output to the bottom pin of the module connector, no need to do the ttl mod.
This bottom pin, on the 'PRO, also supports transmission for the FrSky SPort (XJT module).
Pin 2 of the module connector (counting from the top), is just brought out to the pad labelled 'C'. This connection has been used on the 9X and 9XR to provide a RS232 signal to allow programming of the alarms in a DJT. Since er9x/ersky9x/openTx support providing alarms in the radio firmware, this is not really required, which is why the connection is built in.
You may use a ttl level, non-inverted signal on COM1 on this connection to send serial data. Just below and to the left of the COM1 connector (J18) is the ttl level versions of the COM1 signal. Just wire from J8 pin TX1 to the 'C' pad to get ttl, non-inverted serial data from COM1 on pin 2 of the module connector.
Mike.