Technical Tips


The serial port drives and powers an LCD module of 16X2 characters. Included a VB6 software, PIC C code and a circuit diagram. The communication is RS232 protocol. The VB application transmit only the last input byte to avoid overflow of the receive register of the PIC16F628A.
The serial port can source about 4 mA which is enough to drive the pic and the LCD module. The serial port can't power LCD with LED back light.
You can read more about serial interface in

VB6 code, PIC code and circuit diagram download (20KB). You are free to use the circuit diagram and the VB software with no limitations.

The VB6 application.

Circuit Description
See also Technical Tips

Pin 4 at the serial port is turned to +12V by the software enabling RTS. It is regulated to 5V by 78L05. The 5V is the supply to the microcontroller.
Pin 3 is used to drive RX input, BC337 reverse the signal phase.

LCD display and driver has 14 way connector, 10 connections are used, 4 bits data bus is selected. There is a big selection of LCD modules, and they are very similar in characteristics i.e. DM1601, ACM1601.
Vss - Supply GRD.
Vdd - Supply 5V
Vo - Contrast Adjust
RS - Register Select
R/W - Data Read/Write
E - Enable
D4-D7 - Data Bus Lines
LCD module is 20K pot is the LCD contrast, make sure it is set.