Hard to say, yes the +5v from UNO can cause damage to the LC which is not 5v tolerant. Did you damage it? I don't know.
However sometimes hard to know what is going on, without seeing additional information, like how do you have the two boards connected?
What code are you running on both boards?
I am assuming you are using pins 0, 1 on the UNO, Which pins did you use on the LC? 0, 1 ?
If so I assume you connected 0->1 and 1->0 ?
Did you connect up a common GND between the two boards?
On Uno I assume you are talking the the Serial object? As there is only one Serial object and it shares the USB.
On LC I assume if you are using pins 0 and 1, that you are talking to the Serial1 object?
Testing of the LC. Probably the first thing I would do would be to try running a simple sketch like: the
File->Examples->Teensy->Serial->EchoBoth:
Code:
// set this to the hardware serial port you wish to use
#define HWSERIAL Serial1
void setup() {
Serial.begin(9600);
HWSERIAL.begin(38400);
}
void loop() {
int incomingByte;
if (Serial.available() > 0) {
incomingByte = Serial.read();
Serial.print("USB received: ");
Serial.println(incomingByte, DEC);
HWSERIAL.print("USB received:");
HWSERIAL.println(incomingByte, DEC);
}
if (HWSERIAL.available() > 0) {
incomingByte = HWSERIAL.read();
Serial.print("UART received: ");
Serial.println(incomingByte, DEC);
HWSERIAL.print("UART received:");
HWSERIAL.println(incomingByte, DEC);
}
}
I would then use a jumper wire and connect pin 0 to pin 1 on the LC, and run this program.
In the SerialMonitor, I would type in some text and see if it echoes back.
If it does, this says that it would out Serial1 TX pin and was received back on the RX pin, which is a good sign.
Can you get away with direct connecting the TX pin of the UNO (Pin 1) to the RX pin of LC? I am not really sure, but probably a good idea.
I know some have done things like this by putting in a current limiting resistor to maybe help some. Others have used a couple of resisters as a resister divider to drop the voltage down to the LC.Other times use a TTL level converter... (or simply use a T3.2 which is +5v tolerant).
Good Luck