# UART Communication Issues

I am using a UART to communicate with RS232 on a Roving Networks RN-42 SM bluetooth module. I have the transmitter and receiver connected to a logic analyzer.

The issue that I am having is that my when i connect my uC's TX to the Roving networks RS232 RX, the logic analyzer shows that the TX line of the TX is 0'd. When I disconnect the RX of the roving networks module, it once again starts transferring data.

The images included in the links below.

Here is my transmit code:

while(1)
{
PORTC ^= 0xFF;

transmitStr((unsigned char *)CMDMODE);
_delay_ms(1000);

}


## Connection to TX

• Perhaps you are misinterpreting the "point of view" of the labeling of TX and RX on the module, with the result of connecting the two device's transmit pins together. – Chris Stratton Nov 8 '12 at 19:36
• That is what I thought when it wasn't working but when i checked, it was indeed the TX connected to the RX. I should also mention, the bluetooth moudule is running at 3.3(V) regulated from the 5(V) on the uC. The TX of the uC goes through a resistive divider to get the appropriate 3.3(V) for the input to the RX on the bluetooth module... I don't think that should be causing any issues though – Edwin Nov 8 '12 at 19:41
• Measure with a scope both before and after the divider, that should help you figure out what is going wrong. If you don't have the scope, drive the UART pin as a GPIO toggling every few seconds and use a meter. – Chris Stratton Nov 8 '12 at 20:10
• seems the UART is ALWAYS being pulled high despite the input given to it... I wonder what the issues is... – Edwin Nov 8 '12 at 20:26