RS422 - still with us! My notes

They print nicely - make them full page.

Notes to self - RS422 and balanced audio connectors

I've just finished a job that another SI had done some initial work on. Unfortunately (and although they had used cat5 patch panels) they hadn't used the pinouts that everyone else (Probel, Quartz etc.) uses for sending RS422 over cat5. Anyhow - here are the details in case you ever need to convert. Also - it's best to use the signal earth (pins 4 & 6) rather than the chassis ground (pin 1) - especially if you're running between areas.

Another thing - it's best to use 1/4¨ jacks on mixer inputs as increasingly mixers only have a subset of inputs with XLRs!

Best RS422 tester EVER!

This is the most useful piece of test kit I have ever made! I often have to buzz out RS422 machine controls and since every wireman gets the screens correct (pins 4 & 6 for the Tx & Rx screens) you can rely on them being where you expect. After that it's just a matter of having a 2k, 3k, 7k & 8k resistor on the appropriate pins and you can stick it at the end of the run and see where the pins are missing/swapped over by connecting your multimeter across pins 4 & 6 and the signal pins. I always have one handy (and they often get nicked!)

Adrienne Electronics

Do you remember a BBC2 late-night show called Diners - back in 2002 anything that had the reality label attached to it got commissioned (although admittedly on very late in the evening). If you Google for it now there is scant evidence of it! I did find a John Walsh article from The Independent. Anyhow - one of the problems I had to solve for that show was using cheap Avids (software-only versions - ExpressDV back then) to capture or log live feeds with timecode. Of course the studio or OB sends you audio timecode (the kind that sounds like a fax and comes down a twisted pair cable) but all hardware-less edit stations assumed the timecode comes down the RS422 line as part of the machine control.
Adrienne Electronics do a range of really useful boxes to address these kind of problems - the AEC-Box-2 takes in audio code and has a 9-pin connector. It emulates a VTR but (being a solid box) doesn't actually play or rewind tape - it just tells the Avid it is doing so (in this case it's an Avid MCSoft with SDi Mojo). The really cool thing is that when the Avid asks for timecode down the RS422 the box returns what it is receiving on it's input. It's the ideal solution for using cheap workstations to log or capture proper studio or OB type material.
Now I'd been puzzling about this for ages last night (got home late from the studio where I was working) and it was only over my tea that I remembered solving the problem five years before - kinda like how everyone has forgotten Diners!

Quartz routers RS422 problem

I love Quartz for routers - they are a small English firm (now owned by Evertz) and they really pay attention to detail - like MurrayPro and Crystal Vision you can talk to the designer/programmer and get sense. I see their routers in more OB trucks than most and having put in a few they seem more reliable than Probel et al. The control system and programming tools are very straightforward (Leitch could learn a thing or two!) and the fact you can download to the master level from even a control panel hundreds of meters from the mainframe is fantastic. At MTV last year it saved me lots of shoe-leather!
Now - I put in a simple SDi/RS422 system at five and they had this problem that was hard to replicate - When one of the editors assigned a VTR to one of the Final Cut workstations another VTR route would drop (only on the RS422 level). This meant that in effect they could only use one VTR at a time. I couldn't replicate the fault. Quartz suggested;

• Re-load the router config in case of corruption
• Move one of the VTRs to an unused port and re-programme to reflect the change - in case a cross-point had gone faulty

I tried both of these, but since I couldn't provoke the fault before I started (neither could Stuart, their senior engineer) I felt like I was going through the motions a bit. Stuart even went as far as to suggest it was finger trouble! In the end I saw it happen and it was thus - The editor routes the VTR to the FCP and then he routes the FCP back to the VTR - this is sensible as he doesn't want to have to go back to the control panel when he does his layback. I hadn't appreciated this and had always just routed a VTR into the FCP only for testing. It did seem that when you route a VTR in AND out of an FCP and then do it with another VTR/FCP combo it drops the first route. Everyone at five's reaction was that the RS422 level was having trouble treating each device as a source and destination but this is bogus - even though a VTR is only one hole on the back of the router all P2-protocol devices know about Tx/Rx swaps and that wasn't the answer.
Thinking back to the first or second series of Big Brother I rememeber a similiar problem - it all comes down to the fact that the Quartz control software makes the serial port router look like a set of sources and destinations by using a two-pointer buffer. If you fill that buffer with two routes that refer to the same device you run the risk of subsequent routes breaking that relationship. The solution is to re-sort both source and destination tables so that all RS422 port definitions are in exactly the same places in the tables for the same devices - something you'd never have to worry about for other signal standards. By doing this the buffer never gets monopolised by a single device and the problem is solved.
Now Quartz told me this (reluctanty) back in 2001 and to my suprised it's still an issue - it's also still not documented!

Eyeheight legalisers & RS422 multi-drop

Eyeheight do a great range of products and like Crystal Vision, Quartz, and MyrrayPro they are a small British company who respond to the market quickly. If you have a problem you can probably talk to the guy who designed the circuit!
Anyhow - I was testing a couple of rooms yesterday with OL-2C video legaliser/cages. The control panel and card were in the same chasis in both cases and neither card would accept commands. When I swapped them over one card worked in one chasis but not the other. Clearly something was on the hairy edge and in the end (and I figured this - not Eyeheight tech support!) I discovered the I-CANN bus (the multi-drop RS422 control bus) wasn't terminated on the card - even over that few inches of ribbon cable it made the difference - a jumper on J5 (there is a typo in the manual - it isn't J6) made both cards come good in both boxes.

RS422 over cat5 continued....Back in November I wax'ed lyrical about how I do this - see here - but I didn't reckon on Quartz using RJ45s on their current range of '422 routers - although I satnd by what I said before I'm gonna have to comply on the MTV job!

Rosetta Stone RS422 adaptor re-engineered!

Andy Vasey of AMC does a lot of server integration for us - here is his solution to having proper '422 out of the back of an Intel 2u server case - very ingenious.
It is the board mounted on a half-PCI back plate and then the header from the motherboard's serial connects to the other side.

serial comms -v1.pdf
First stab at an RS422 & 232 reference for broadcast engineers and wiremen for possible inclusion in the technical help section of the new Root6 catalogue.

RS422 over cat5 cable
I cable a lot of TV facilities and the tendency nowadays is to use the ubiquitous cat5 data cable for carrying everything that doesn't require a better grade of cable. RS422 for machine control used to be universally carried on Star Quad cable but now cat5 does the job - here is the pinout I have settled on:

• I avoid the blue pair because that is often used to analogue voice and if you mis-patched you may wind up terminating a data pair in a low impedance.
• The brown pair often carries power in POE (Power Over Ethernet) implementations and if you mis-patch the sending switch sees a low impedance and shuts off the current.
• The orange and green pair carry the Tx and Rx pairs as per ethernet (which expects to see a 110 ohm termination).

That's why I do it thus!

AEC-BOX-1/2/10/20 Stand-Alone LTC/VITC Time Code Reader
This unit allows you to have an application that can't read audio or vertical interval timecode but can drive a VTR down an RS422 connection - typ. Avid ExpressDV etc. The box spoofs a VTR and returns timecode when asked either from it's XLR input or by extracting it from the VITC - an application I've ued it for is logging "live" video (i.e. MediaLog on reality shows).