![]() By alternating the data transmitted from the computer between the bit-bang values sent to LP0 and 0xF0 sent to the serial connector the eight parallel data bits become fully addressable. That’s where the serial connection comes into play. ![]() Thyristors are bistable switches so this solution alone will never clear the busy pin. The strobe pin on the parallel port drives an inverter which triggers a thyristor connected to the busy pin. Instead the USB to RS232 (serial) converter also pictured above is used as a reset signal. All you need to do is program the chip to emulate the printer’s end of the communications scheme. Sure, adding a microcontroller would make this dead simple. It borrows from the way printers communicate to allow USB to parallel port bit banging without a microcontroller (dead link, try Internet Archive). But here’s a solution that will change your thinking. If you’ve ever looked into low-level parallel port access you may have learned that it only works with actual parallel port hardware, and not with USB parallel port adapters.
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