Electronic – What causes a UART device to continuously repeat its last transmission

bluetoothftdiuart

I just got this awesome Bluetooth module in the mail. I connected power and UART pins, and tied pin 34 to +3.3v with a 1k resistor (that puts the module into AT command mode rather than pass-through bluetooth mode).

So the first thing I notice is that it's sending "ERROR:(0)" repeatedly at about 15 messages per second. But if I send a character, it stops. If I have stopped it, then I can send an AT command such as "AT" followed by enter. The module proceeds to then send "OK" repeatedly at 15 messages per second.

I'm going through all the supported AT commands, and each one works, but it continuously repeats itself until I press the any key.

I tried connecting the CTS/RTS pins but it acts the same way as when I just use the UART pins alone.

I'm connected to my PC via USB FTDI UART cable that basically gives me a serial port on my PC (/dev/ttyUSB0) and a uart header on the other end, which I have connected the module to.

When I send the AT commands, I am getting valid responses, it's just that I have to press a key to stop it from sending its response over and over, and that key gets thrown away.

Seems really weird, but I bet there's a good explanation out there?

Best Answer

It sounds like you've connected TX and RX together.