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Based on the FtMscLib API (chapter 6: BT-API) and in online mode, I try to write a program for a TX-C (Master) that is able to communicate with another TX-C (Slave) with a RoboPro program.
The RoboPro based programming is receiving and transmitting messages.
The BT-API program act as master.

I am able to establish the BT-connection with the Master and the Slave.
However I don't receive the messages from the RoboPro program.

How to use the BT API is not my problem, two online TX-C with both using and BT-API based program running well.
How to use RoboPro BT messages is also not my problem, two online TX-C with both a RoboPro based program program running well too.

Suggestions will be welcome.

Receiving with the BT-API based program at the slave site was not too difficult,
however I still was not able to resolve this at the master site:

message size 6 bytes
[1] RCN
[3][2] command encode; 3 symbols into 2 byte "a " 00 01, with for "=" FF F9

The line with 0 are transmitted to keep the connection alive.
[0] is sometimes 00 and sometimes 02 ; why???

BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 03 [2] 41 [3] 06 [4] 00 [5] 7F
BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 00 [2] 00 [3] 00 [4] 00 [5] 00
BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 00 [2] 00 [3] 00 [4] 00 [5] 00
BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 00 [2] 00 [3] 00 [4] 00 [5] 00
BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 00 [2] 00 [3] 00 [4] 00 [5] 00
BtReceiveCallback =BT_MSG_INDICATION channel=1 mesg=6 [0] 00 [1] 00 [2] 00 [3] 00 [4] 00 [5] 00