Need to run at least 7 (maybe more) samplers from a single computer port.
Would like to do it from ttyS1 (com2) but am more familiar with using an ADC off of parallel (printer} port but cannot find enough I/O lines (/registers) to do it (via bit banging) with the serial port. Any help on this part??
Am intending to start with just 1, 8-bit chip off of the parallel port. Problem is this: some devices will be serviced every minute others at 5, 10, 15, 20, 30, and/or 60 minute intervals. The selected device will be fed to the ADC via this multiplexer. Now I think I know the difference between synch and asynch but with multiplexer chips I am unsure what that means exactly. Does it mean that if the chip is synchronous that the clock must be strobed via a separate clock on a regular basis? I expect to select the channel on the appropriate chip (if more than 1) feed the ADC by strobbing the bits off of the ADC then go to the next device. Can someone clearify the synchronous vs asynchronous multiplexer question for me??

 

Need to run at least 7 (maybe more) samplers from a single computer port.

Samplers for analog data, in digital form?

When I hear the term "samplers", it implies (to me, anyway) digital musical instruments (generally keyboards) that are capable of recording and playing back sound samples of "real" musical instruments for recordings or live performance. You may simply be referring to digitized samples of analog data, or something completely different.

Would like to do it from ttyS1 (com2) but am more familiar with using an ADC off of parallel (printer} port but cannot find enough I/O lines (/registers) to do it (via bit banging) with the serial port. Any help on this part??

RS232 and LPT ports are legacy items at best. You really should investigate using USB or FireWire ports, as otherwise you will soon find nothing to plug your stuff into.

Am intending to start with just 1, 8-bit chip off of the parallel port.

Give up on the parallel port idea. That's 1980's technology. It was fun while it lasted. There is no point in creating something new for a technology that is dead.

Problem is this: some devices will be serviced every minute others at 5, 10, 15, 20, 30, and/or 60 minute intervals. The selected device will be fed to the ADC via this multiplexer.

OK, now you have a problem. Multiplexers are not low impedance devices. You will need an input voltage follower/buffer to provide a low-impedance signal source, and a high-impedance output voltage follower/buffer to minimize the effect of the mux/demux.

Now I think I know the difference between sync and async but with multiplexer chips I am unsure what that means exactly. Does it mean that if the chip is synchronous that the clock must be strobed via a separate clock on a regular basis? I expect to select the channel on the appropriate chip (if more than 1) feed the ADC by strobing the bits off of the ADC then go to the next device. Can someone clearify the synchronous vs asynchronous multiplexer question for me??

With an asynchronous mux/demux, when you change any pin's data on the address select lines, the I/O path is changed.

With a synchronous mux/demux, the address is selected from the state of the address pins when the clock is toggled. To make the synchronous address select more reliable, the address data is normally placed on the address select lines out-of-phase with the clock.

 

Samplers are composed of data acquisition device, digitizing device and recording device, aka data loggers. I am a long term scientist and prefer the term sampler as that is what it is doing.

I realize to you that com ports and para ports may be antiquated but if they exist on the boards as of 2007 then perhaps you are younger than you think <);^)

I am just getting back at the dum-As that came up with something (USB conversion cables) that is costs another $30 which is a pain to try to program and requires another post graduate degree to figure out if is the correct one for the purpose. Some cables cannot be programmed you know. Even if one can program same the buggers have a delay in them which negates their use in emulating a paraport or a com port (com for Wndows people) for high speed data collection, i.e. 1.25ms.

As I am not an engineer you have confused the issue for me with reference to "address select" line. Are these the 3 S0-S2 lines of a CD4020 for example? If so then how is a CD4020 different from a 74HC164 because those 3 lines control which port /channel is selected and does so when the clock is strobed for both those chips?

 

Perhaps you could let us know of the precision required. If an 8 bit conversion is adequate, there are very low cost 8 and 10 bit dataloggers (thats what we called 'em at the University of Missouri) available from Dataq. I've got the DI-154 & 194 loggers.

They are serial port devices. Not real flexible, but you can always see if they fit the need (we have as yet no idea of the nature of the analog signals to be converted) - http://www.dataq.com/194.htm

If you need precision and flexibility, the DI-710 is a reasonable choice. It is a USB device, which makes it computer-independent. Parallel ports are no longer to be found. As soon as the legacy device base shrinks, the serial port will be eliminated. Mammon outvotes utility and convenience.