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Groups > comp.arch.embedded > #31324
| Newsgroups | comp.arch.embedded |
|---|---|
| Date | 2022-11-03 13:32 -0700 |
| References | <6b8c6b92-a2ca-4849-ba68-f03060bc41fcn@googlegroups.com> <tk15a0$usu$1@gioia.aioe.org> |
| Message-ID | <34f51ec8-9265-4cfa-93ff-c65eb0050fbbn@googlegroups.com> (permalink) |
| Subject | Re: Shared Communications Bus - RS-422 or RS-485 |
| From | Rick C <gnuarm.deletethisbit@gmail.com> |
On Thursday, November 3, 2022 at 3:37:43 PM UTC-4, Dave Nadler wrote: > On 11/2/2022 1:28 AM, Rick C wrote: > > I have a test fixture that uses RS-232 to communicate with a PC. It actually uses the voltage levels of RS-232, even though this is from a USB cable on the PC, so it's only RS-232 for maybe four inches. lol > > > > I'm redesigning the test fixtures to hold more units and fully automate a few features that presently requires an operator. There will now be 8 UUTs on each test fixture and I expect to have 10 to 20 test fixtures in a card rack. That's 80 to 160 UUTs total. There will be an FPGA controlling each pair of UUTs, so 80 FPGAs in total that the PC needs to talk to. > > > > Rather than working on a way to mux 80 RS-232 interfaces, I'm thinking it would be better to either daisy chain, or connect in parallel all these devices. The protocol is master-slave where the master sends a command and the slaves are idle until they reply. The four FPGAs on a test fixture board could be connected in parallel easily enough. But I don't think I want to run TTL level signals between so many boards. > > > > I could do an RS-422 interface with a master to slave pair and a slave to master pair. The slaves do not speak until spoken to, so there will be no collisions. > > > > RS-485 would allow all this to be over a single pair of wires. But the one big issue I see people complain about is getting PC software to not clobber the slaves, or I should say, to get the master to wait long enough that it's not clobbering it's own start bit by overwriting the stop bit of the slave. I suppose someone, somewhere has dealt with this on the PC and has a solution that doesn't impact bus speed. I run the single test fixture version of this at about 100 kbps. I'm going to want as much speed as I can get for 80 FPGAs controlling 160 UUTs. Maybe I should give that some analysis, because this might not be true. > > > > The tests are of two types, most of them are setting up a state and reading a signal. This can go pretty fast and doesn't take too many commands. Then there are the audio tests where the FPGA sends digital data to the UUT, which does it's thing and returns digital data which is crunched by the FPGA. This takes some small number of seconds and presently the protocol is to poll the status until it is done. That's a lot of messages, but it's not necessarily a slow point. The same test can be started on every UUT in parallel, so the waiting is in parallel. So maybe the serial port won't need to be any faster. > > > > Still, I want to use RS-422 or RS-485 to deal with ground noise since this will be spread over multiple boards that don't have terribly solid grounds, just the power cable really. > > > > I'm thinking out loud here as much as anything. I intended to simply ask if anyone had experience with RS-485 that would be helpful. Running two wires rather than eight would be a help. I'll probably use a 10 pin connector just to be on the safe side, allowing the transceivers to be used either way. > > > Hi Rick - I have an RS-485 system on my desk using an implementation of > the old Intel BitBus. Works fine for a handful of nodes, limited > distance, and very simple cabling - but only 62.5kbaud. Good solid > technology for 1994 when I designed it... > > Why would you use RS-485 instead of CAN? A million chips out there > support CAN with no fuss, works at decent speeds over twisted pair, not > hard to use. > > BTW, another option for interfacing to RS-485 from USB is XR21B1411 > which is what I happen to have on my desk. I'm using RS-422 because I don't need to learn how to use a "chip". It's the same serial protocol I'm using now, but instead of RS-232 voltage levels, it's RS-422 differential. The "change" is really the fact that it's not just one slave. So the bus will be split into a master send bus and a slave reply bus. The master doesn't need to manage the tri-state output because it's the only talker. The slaves only talk when spoken to and the UART is in an FPGA, (no CPU), so it can manage the tri-state control to the driver chip very easily. CAN bus might be the greatest thing since sliced bread, but I am going to be slammed with work and I don't want to do anything I don't absolutely have to. A lot of people don't understand that this is nearly the same as what I'm using now and will only require a very minor modification to the message protocol, to allow the slaves to be selected/addressed. It would be hard to make it any simpler and this would all still have to be done even if adding the CAN bus. The slaves still need to be selected/addressed. Thanks for the suggestions. The part I'm worried about now are the more mechanical bits. I am thinking of using the Eurocard size so I can use the rack hardware, but I know very little about the bits and bobs. There will be no backplane, just card guides and the front panels on the cards to hold them in place. I might put the cabling on the front panel to give it easy access, but then it needs machining of the front panel. I could simplify that by cutting out one large hole to expose all the LEDs and connectors. I want to make the design work as simple as possible and mechanical drawings are not my forte. -- Rick C. -+- Get 1,000 miles of free Supercharging -+- Tesla referral code - https://ts.la/richard11209
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Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-01 22:28 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 10:28 +0100
Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-02 11:54 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 14:27 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 12:20 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 21:49 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 16:27 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-03 12:42 +0100
Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-03 14:00 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-03 16:26 +0100
Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-04 08:45 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 10:49 +0100
Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-04 15:37 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 17:36 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 10:11 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 11:58 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 09:55 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:00 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-07 15:46 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:05 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-07 19:02 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 17:15 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-08 06:54 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-08 05:50 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Clifford Heath <no_spam@please.net> - 2022-11-09 10:45 +1100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-08 16:46 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Clifford Heath <no_spam@please.net> - 2022-11-09 22:32 +1100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-09 04:53 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-09 23:45 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-09 21:42 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 08:40 -0700
Re: Shared Communications Bus - RS-422 or RS-485 antispam@math.uni.wroc.pl - 2022-11-04 22:53 +0000
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 18:07 -0700
Re: Shared Communications Bus - RS-422 or RS-485 antispam@math.uni.wroc.pl - 2022-11-05 03:46 +0000
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 02:09 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 10:40 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 12:47 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 10:23 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 19:57 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 13:42 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-06 11:55 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-06 05:56 -0800
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-06 21:53 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 01:58 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:26 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:39 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 12:07 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:25 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 17:57 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 09:50 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 21:30 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 14:27 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-08 00:07 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 16:50 -0800
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-08 09:02 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-08 06:58 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-06 18:34 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-06 15:37 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-06 19:18 -0500
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:07 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:03 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:55 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:18 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 18:20 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 10:26 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 22:04 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 14:54 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-07 15:14 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 16:57 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 07:51 -0800
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 08:29 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 10:36 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 12:32 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 13:08 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:40 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 16:50 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 21:10 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 11:13 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 08:52 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-04 20:03 -0700
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 17:25 +0100
Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 11:01 +0100
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-02 15:00 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 16:31 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-02 17:36 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 21:58 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 09:57 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 12:02 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 12:53 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:33 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Dave Nadler <drn@nadler.com> - 2022-11-03 15:37 -0400
Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:32 -0700
Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-04 22:47 -0400
Re: Shared Communications Bus - RS-422 or RS-485 chris <chris-nospam@tridac.net> - 2022-11-05 00:13 +0000
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