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I just bought the serial 7-segments LED display last week and using serial TTL communication with 3 wires connected to VCC, GND and RX.
The wires connection was double checked and in best condition.

The code in VB.Net to open the RS232 ComPort in 9600, N, 8, 1 is good and test in other device already.

I am trying to send number 1, 2, 3, 4 to let LED to display "1234", it always display "0000"!

Following is my code for sending the data to LED module:

Dim WithEvents RS232 As SerialPort
'Open the RS232 ComPort
RS232 = New IO.Ports.SerialPort(COM1, 9600, None, 8, 1)
'Send out data
Dim xmtSend() As Byte = {&H31, &H32, &H33, &H34}
RS232.Write(xmtSend, 0, 4)

Please help!