Extending serial (RS232/422/DMX) over long distance

Here's a little video showing how to use the Barnfind BarnMini05 to extend serial control over very long distance using wavelengths on a single mode fibre.

 

RS422 serial control via MOXA industrial control cards

My word - two years since I last updated this blog; I'm covered in shame...

So - currently configuring a workstation that needs to capture from up to eight VTRs simultaneously. The recommendation from the software vendor (METUS Ingest) is the MOXA CP-118EL-A which is eight serial ports on a 4-lane PCI-e card. I've used other MOXA products in the Electric Friends camera robots we installed in Studio B at BBC New Broadcasting House and they are proper industrial parts that look like they'll last for decades!

So, there are two things to bear in mind when using one of these cards with video apps (and hence old-school VTRs); even in RS422 mode they do use the Sony 9-pin D(m) pins for the Tx and Rx pairs (and the signal ground).

So, wire your cables thus;

Although you'll find the ports in Windows device manager, you will need to go into the settings for the multi-port serial adaptor to make sure they are set for RS422 rather than RS232.

Quick & dirty RS422 VTR control from your laptop

If you need to control a deck (or test routes through an RS422 matrix) then a very quick and easy way of doing it is via your laptop. Modern machines don't have RS232 ports and so you can't just hook up an RS232-422 balancer, but USB serial devices are cheap - the Addenda RS-USB4 is the one I keep in my rucksack.

It's worth noting some of the settings you need for the serial port in Windows.

You then need a bit of software that will talk the P2 protocol. WSony II has been around forever but still works under Windows7. You have to run it as admin for it to access the serial port.

Once it runs you have to tell it what port number gave it - It shows up as Com1 on my machine by default, but bear in mind that Windows will often assign it to Com5 or greater. The WSonyII will only talk up to Com4 so you might need to change that (see the first image above in the advanced tab).

Now you've got everything you need to drive a VT or test that an RS422 circuit is working.

Oh, if you don't have the CD that came with the Addenda adaptor cable you'll need to download the software here.

Remember; P2 over RS422 runs at 38,400 baud.

Chassis vs Signal earth on RS422 remotes

Grounding is essential to reliable operation of any RS422 connections. It is also the most overlooked and least understood. The easiest way to ground your RS422 equipment is to simply use "Earth" ground as your return path. Although easy this may not be the best method for grounding your application, because current leaking from equipment, electro-static discharge (ESD), and lightning all drive current through this path which results in high noise content. The reason for this increased noise level is due to the fact that "Earth" ground presents a relatively high resistance. RS422 is designed to operate normally with a ground potential difference of +/- 12 Volts. During normal operations this is typically not a problem, however during fault conditions or lightning strikes even within ½ mile the ground potential difference can reach hundreds and in some cases thousands of volts. This will most likely result in damage or failure of one or more devices on the RS422 router.

In TV facilities I most often come across three methods of earthing;

1. No earth - assume that the mains return is good (all equipment is class-1 and bolted into it's bay and that signal and chassis earths will be close)
2. Use pins 1 and/or 9 on the 9-pin D-type to couple the chassis earths together; please, don't get me started about intentionally connecting mains earths between different areas! Do you like dealing with induced hum between different areas or buildings?!
3. The best way; using pins 4 & 6 - the signal screens (it's what they're there for).

The job I'm finishing at the moment had a problem with Digital Rapids workstation which wouldn't run through the RS422 router although patching around the router worked - the PC could control a VTR. My first port of call was to test the cabling/router patch by sticking an old Sony RM450 edit controller at the back of the Rapids and pretend the RM450 was the workstation - all good; VTR control and timecode return worked fine (so Tx and Rx doing their things). 

So my first thought was to measure the impedance between the signal ground on the router and the mains earth - high Z so no return patch for the RS422 via the router if it was relying on the mains earth (scenarios 1 & 2 above) and since the router is optically isolated on it's data inputs I wasn't surprised. That is the way it should be done.

Now then; most PCs that are running video apps and have to control a piece of broadcast kit use an RS232 port with an external RS232-422 adaptor. These essentially just balance the Tx and Rx pins and there are several models. None of them (in my experience) actually use a pair of rep coils to properly balance rather they use a pair of op amps in a differential input configuration. This is fine but doesn't have the noise immunity that you get with coils (common mode rejection). What it does mean is that all of the noise immunity of the circuit comes from the electrostatic shielding of the earth and so you better get it right!

I cracked open the cheap'n'cheerful '232-422 adaptors supplied with the rapids and they had the screen connected to the shield of the 9-pin on the RS422 side (so relying on scenario 1 above). Moving that to pins 4 & 6 (scenario 3) fixed the problem. 

As an aside the Adenda "Rosetta Stone" adaptors that Avid supply do the right thing!

How to do RS422 properly on the big Blackmagic Universal Videohub?

A job we're working on at the moment needs a big 288x288 HD/SDi and RS422 router. Budget means that the Black Magic is the only one that can be considered and it's hard to argue with sub £100k - Probel, Quartz-Everts etc would all cost four times that amount and so we're trying to figure out how to cable this one nicely.

The issue is going to be with the RS422; video will dress nicely on the cable tray down each side of the cabinet but the remotes are presented on a proprietry connector in the centre of each card. The only way of connecting to this is via a pre-made breakout cable that in only a metre long. So, after a lot of thinking and measuring we've come up with a solution.

 So far I've not been able to locate this connector - anyone have any thoughts?!

 Chopped breakout cable to see what the colour code of the cores is.

Nice 1/2u high cat7 jackfield which we'll use (need a dozen of them) to run down the intermediate rackstrip at the rear of the matrix to allow proper RS422 breakout.

The colour code we've settled on for this router when it's being cabled on cat6.

RS422 / Sony P2 protocol and serial stuff!

When running P2 protocol over RS422 (i.e. Sony VTR remotes) there is no hardware handshaking so RTS and CTS (Request To Send and Clear To Send) aren’t used; a bit like the old 3-wire XModem/YModem/Kermit protocols used in RS232 (remember RS422 is just a balanced version of RS232).

We base our RS422 wiring on the Quartz remote standard (Quartz were one of the first firms to use RJ45s & cat5 for RS422 remotes):

However – I know for certain that Probel use a different standard and many places are wired to whatever the local standard is; remember – until ten years ago most places wired ‘422 on star-quad cable rather than cat5e/6. I don’t know if current model Evertz routers have maintained the Quartz standard – I bet they have given they bought Quartz for its router business.

Whatever wiring standard is used always make sure that pins 2 & 7 are a twisted pair and likewise 3 & 8 otherwise you lose all the advantage of common-mode noise rejection that balanced RS422 brings.

Finally you need to be certain if a place is wired for chassis earth (pin 1 on a 9-pin) or signal earth (pins 4 & 6 on 9-pin). Signal earth is best as there is always a chance of earth-hum between areas when you tie chassis earths together but hopefully properly designed kit with balanced lines have the signal earth floating WRT to power/chassis ground. BUT, you have to stick with the local standard; if the engineer has wired only chassis earths you need to continue using pin 1 or even shorting pins 1, 4 & 6 at the remote end.

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).