cmos - ttl problem

[moe2k3]

I have to connect this temperature sensor to the PCs parallel port. So I connect the sensor to adc0804, which I think is CMOS based. Next I need to connect the 8 bits to the PCs parallel port. So I use 2 quad bus buffers, 74125. The buffer is ttl-based. The pc's parallel port considers 5V as on and 0V as off. So theres nothing wrong with the buffer.

But how can i connect the ADC0804 with the rest of the ttl-based circuit.

 

[BrianG]

You can't just connect the adc0804 to the buffer chips: first you have to design some control logic to make it perform the a to d conversions. Then you need to understand how the PC parallel port and its control line handshake works, because you will need to design some control logic for that bit in order to get the data from the adc into the port.

Suggest you find a book on the IBM PC hardware.

 

[IRstuff]

As to your specific question, CMOS chips are usually designed to drive at least 1 standard TTL input, so once you figure out the rest of your circuitry, the outputs from the A/D can drive the bus driver inputs directly.

Otherwise, what would be the point of using bus drivers to drive loads you can't drive, if you can't even drive the bus driver? TTFN

 

[jbartos]

Suggestion: Also, a suitable 8 bit parallel I/O card appears to be needed.
What about using a fast USB? Visit

http://www.picotech.com/data.html#temp

 

[Chuckles159]

If your CMOS output will not drive a TTL load, look up the CD4050 as a possible buffer. However, standard CMOS will drive one standard TTL load. On the other hand, as long as the supply voltage is the same TTL can drive all the CMOS you want.