Technical Tips


A project of connecting LCD display module to LPT printer port with multi lines and adjustable characters number. Included a VB6 software, Visual Studio 2005 VB and a circuit diagram. There are several makes of this module that are interchangeable, the one I used is UC-16207. The LCD module has a 14 way connector, 8 pins are used for data, 2 for supply, register select(RS), read/write, enable (E) and contrast adj. The R/W input must be connected to earth to make sure that data lines are in input mode. The VB application has only basic functions, it can be changed to interface the display for a variety of inputs.
The LCD module requires a delay of 2 ms or longer for some of the commands and clock (Enable) of 10 us or longer. By loop counting during Timer1 of 100 ms interval the speed of the cpu can be assessed and used to set micro-second time base.
The io.dll file has to be in the same folder as the exe file.
You can read more about LPT interface in

The download includes a freeware DLL (io.dll) which can be updated from
Keep the .exe file and .dll in the same folder. You are free to use the circuit diagram and the VB software with no limitations.

PC application.

Circuit Description
See also Technical Tips

5 volt supply can be an external power supply, using the hosting computer 5V is much preferred because variation between the computer 5V and the external 5V can lead to undesirable currents through the data lines. 5 volt supply is available at a USB port or the 4 way peripherals connector from the internal power supply unit.
Module can work with voltage range of 3.3 to 5 volts. Below 5 V the module doesn't initiate on power up so the VB extra instructions have to be enabled.
20K trimmer is needed to adjust the contrast voltage which vary with different batches of LCD.

Pins 7 to 14 of the LCD are data inputs. Pin 6 is clock input, enables LCD module to read the data.
Pin 4 is Register Select input, it is used for 16 bits instruction.