circuit help wanted

[mstechca]

Look at the picture. This circuit works if I connect the inputs to +5V or 0V and the outputs to LED's in series with 330 ohm resistors.

However, when I connect the circuit to the parallel port, and tried sending data, the busy flag is continuously on, and when I tried monitoring the strobe signal with an LED, it seems that nothing happens.

In a typical parallel port (inside the computer), what pins are connected to pull-up or pull-down resistors, and what are their values?

why? because I will then redo the default logic levels to match my design. Default levels means the level you get when nothing happens. For the strobe signal, the default level is high since nothing happens.

It kills me how a 100% working design can turn into a 0% working design.

I should mention that I'm trying to program an At89C2051 microcontroller, and the clock I am using is an astable multivibrator with transistors that has a 1 mS clock rate.

I know that value is long, but if I can program at least 10 bytes without any data missing, then I will be happy.

 

[Roff]

What's the part number on those tri-state buffers?

Edit:
It just dawned on me that 2k is marginally too high to sink the logic LOW current of an LSTTL device. If you were using HCMOS, it would work fine. If you want to stick to LSTTL, I would change it to 1k or less. That, of course, may not solve the problem.
Why not clock the LS164 directly, instead of through that buffer?

 

[mstechca]

the buffers are I think 74HC125E.

For the input clock, it is an astable multivibrator with 2 npn transistors. The default level is a logic high, and since the clock on the 164 requires a positive edge, I want to turn the default level to a logic low so that the clock does not get accidently activated.