Multiplexers suitable for computer ports? - Page 1
Forum section: electronics / beginners

author: analogix
author_rank: Frequent Contributor
timestamp: December 30, 2024, 04:46:55 pm
content: Thanks toreplies to this this threadI've learnt a lot about multiplexers.That thread is about switching VGA video signals to different outputs, and from what I've read there are "analog switches" that can switch both analog and digital signals, and there are "digital multiplexers" which are only for digital signals.Is it safe to assume that while the analog ones introduce a switch resistance (Ron), the digital variants don't, as the switching doesn't mimick a physical switch but acts in a different way, and this is the way to go if you're dealing only with digital signals?Finally, while searching for a suitable digital multiplexer it seems they're only available with up to 8 inputs or less. Is this correct, or have I been searching for the wrong type of component? I'm looking for something to switch various computer port signals consisting of up to 40 signal lines or so.

author: PGPG
author_rank: Frequent Contributor
timestamp: December 30, 2024, 06:36:44 pm
content: Analog multiplexer introduces in signal path some Ronand digital multiplexer introduces in signal path some time delay.What is better can depend on many conditions.You can even use relays to switch wires directly.

author: wraper
author_rank: Unknown
timestamp: December 30, 2024, 07:09:38 pm
content: Don't look for general stuff. Look for multiplexers/switches designed for particular port types.QuoteNo. While some may be something else, most of them are just low impedance analog switches. Particular port types require certain specs, such as impedance, capacitance, voltage range.

author: analogix
author_rank: Frequent Contributor
timestamp: December 31, 2024, 12:46:38 pm
content: Quote from: wraper on December 30, 2024, 07:09:38 pmYes, having read about that in theTexas Instruments Application note -Multiplexers and signal switches glossarydocument I further looked upTexas Instruments' protocol specific switches and muxes, but it appears they only cater for currently used computer ports (USB, HDMI etc.).And web/forum info on the subject seems quite complex, but I'm quite possibly looking up other scenarios in my ignorance, adding to the confusionIn my case they're ports on an Atari STe (80s/90s vintage computer), and I'm not totally sure if Atari followed established protocols back then either. I know for a fact that some of the ports were "almost" up to standards (like the video output which is "almost VGA", and the ACSI hard-disk port which is "almost SCSI"), so protocol specific MUX chips might not be the solution here? ......Here are the specific ports I want to add switching to, and how:1. Atari modem (serial) portA serial to MIDI converter will be attached here. But I also want to be able to occasionally use the serial port as normal -hence the need for a 2-way switch.(Serial pinout source:Info-coach)2. Atari cartridge portThis port will connect to multiple hardware add-on expansion devices and copy-protection dongle cartridges. Unfortunately they don't all work well together (and frankly, I don't even need to have them all available at once), so I've grouped them into chains that do work. I also have an empty cartridge port for attaching whatever I need at the time. So here I want to switch to whichever cartridge "group" I need to use, hence the need for a 4-way switch.(Cartridge pinout source:Info-coach)3. ACSI (hard disk) portACSI(Atari Computer System Interface) is an "almost SCSI" standard. I will attach an ACSI to SCSI interface to this port (so as to be able to use standard SCSI hard drives etc.), but I also want the option to occasionally use the port as the original ACSI (some add-on expansion Atari devices utilize ACSI), hence the need for a 2-way switch.(ACSI pinout source:Info-coach)

author: Siwastaja
author_rank: Super Contributor
timestamp: December 31, 2024, 02:03:32 pm
content: Unfortunately, as wraper pointed out, there is no generic answer; suitable multiplexer is per port type.

author: analogix
author_rank: Frequent Contributor
timestamp: January 01, 2025, 03:29:37 pm
content: Quote from: Siwastaja on December 31, 2024, 02:03:32 pmDoes this mean I first need to fully understand the specifications/behaviour of each signal line of all three computer ports before being able to find a suitable MUX chip(s)?I was thinking that it was just a matter of switching each signal (except perhaps the GND line which would be permanently connected to both outputs), then finding a MUX with the amount of switches I need (or multiple MUX chips if each of them don't have enough switches).