Any idaes why my PIC/ parallel port communication so slow?

[JohnJohn20]

Hi. I have a PIC oscillating at 1MHz. It takes ADC readings and transmits them to my laptop via the parallel port.

The PIC board communicates by toggling two of the parallel port high and low using opto couplers.

So to send a high bit, both pins would go low (for ~1ms) then both high (pulse finished signal, for ~1ms) and to send a low bit, one pin goes low (for ~1ms) then both go high (for ~1ms).

I use a qbasic program to watch these pins and waits for their state to change.

If I send through a 67 bit data stream (that is 134 changes of state) I can't send it any faster than 0.11 seconds. That is, I can't make the pulses any shorter than 1ms. Any suggestions why?

I have read that the parallel port is capable of 12Mb per second. My laptop is old (it has a parallel port!) with a 1.3GHz celeron processor.

Thanks. Chris.

 

[yura717]

Enhanced Parallel Port (EPP) was created by Intel, Xircom, and Zenith in 1991. EPP allows for much
more data, 500 kilobytes (KB) to 2 megabytes (MB)
The maximum speed of the Centronics interface is 150 kilobits per second, though Interfacebus.com contends that the cable typically offered no more than 10 kbps connectivity.