BX310x cannot transfer binary data over BT SPP

I am trying to send binary data over BT SPP and it seems like the chip can only do ASCII even when I am in data mode. The binary data I am trying to send is the MODBUS protocol.

Firmware version : BX310x.2.6.3

Communication : UART, 115200, 8 data bits, No parity, 1 stop bit, hardware flow control enabled (AT&K3)

AT command sequence:












// After this, the remote device discovers the module and requests to open a SPP connection. Here are the notifications I get:

+SRBTPAIR: “6c:00:6b:73:20:c0”, 1

+SRBTCFG: 1,0, “6c:00:6b:73:20:c0”,SPP,0


// Once I receive the +SRSPPCNX notification, I set the SPP connection to data mode:


I don’t have a console log for the data bytes, but I have a logic analyzer that shows the data bytes being sent to the UART port of the BT module. I have attached a screenshot with timestamps

As for AT+SRSPPSND command, the reference manual states that it only supports ASCII. I need to be able to send the full unsigned 8-bit range of binary data 0-255. This isn’t possible unless we send individual digits encoded in ASCII. While this may be ok for newer applications that can parse ASCII, it will not be a drop-in replacement for existing applications that accept binary only. I think this limits the applications with this chip by a lot and a firmware fix for this should not be too difficult.

Please advice

Hi @vipul.vishnoi,

This is the limitation of the current module. Sierra is also aware of this issue. I think new firmware release will be updated soon to fix the issue. "