PC Oscilloscope via LPT Port

The oscilloscope utilizes the SPP or EPP parallel port LPT1 for reading the data from ADC0820 (TLC0820).

The program will automatically switch the LPT1 in byte mode or normal mode if the LPT is an ECP type. Upon starting the program, there is a software test which checks of the hardware will let the software set the bit 5 of the control byte of LPT. The LPT port can be placed in the bidirectional mode by setting the bit 5 of the control port to logical high. Bidirectional ports cannot only output data but the port can also read data, although not all parallel ports are bidirectional.

In case someone tries to connect to a non-bidirectional port, those 1K Ohm current limiting resistors are placed between ADC and LPT. For analog input protection, 10K, 1M resistors, 1N4148 and ZD5V are added. The supply voltage of the ADC should never be exceeded by the analog input at the pin 1. A resistor divider between signal and ADC should be added when measuring the signals with amplitude more than 5V, to keep the voltage below 5V at pin 1. ADC must be synchronized with the PC.