Why would only certain RS232 controllers work? - Page 1
Forum section: electronics / testgear

author: jonnyGURU
author_rank: Contributor
timestamp: September 10, 2021, 06:06:53 pm
content: Wasn't sure this was the right sub-forum, but since it IS for test equipment.....I have an ATE (a SunMoon SM-8800 DC load tester) that interfaces with an RS-232 (DB9). Tried using a USB adapter did not work. No communication.Team member has same ATE and uses it with a really old Compaq with native DB9 serial ports and it works.Reached out to ATE manufacturer and they suggested using a desktop PC with an add in card. Specifically, this one:https://24h.pchome.com.tw/prod/DCAD4M-A42400149Now, I don't mean to be stubborn, but I'd much rather use a laptop with the ATE then have a dedicated PC for it.Anyone figure out why an add-in card or native controller would work, but a USB adapter wouldn't? Pin out is the same. Protocol is RS-232. I just don't get it.Thanks all!

author: Bassman59
author_rank: Super Contributor
timestamp: September 10, 2021, 06:18:31 pm
content: Not all USB-to-RS232 adapters are the same.Perhaps the ATE requires the use of the flow-control signals and your USB thing doesn't have them?

author: PeteH
author_rank: Unknown
timestamp: September 10, 2021, 06:19:31 pm
content: Speeds? Cable length?Rs232 adaptors get heavily loaded by cable capacitance.Older rs-232 designs may have +/-12V levels vs most usb to rs232 adaptors having charge pumped 3.3v +/- rails, so much lower peak-peak voltage, means the duty cycle of received data waveform becomes distorted with load capacitance as the thresholds are not symmetric about 0VDC.

author: jonnyGURU
author_rank: Contributor
timestamp: September 10, 2021, 06:28:13 pm
content: Quote from: Bassman59 on September 10, 2021, 06:18:31 pmI thought about this and was considering getting a RS-232 "tester" and putting it in line with the Compaq, and then doing the same test again with the USB adapter.Something like this?https://www.amazon.com/Breakout-Tester-Monitor-Female-Module/dp/B08CDQ76Q8/

author: Karel
author_rank: Super Contributor
timestamp: September 10, 2021, 06:30:32 pm
content: Could be a USB suspend mode issue. I recently had a problem with an FTDI USB<->RS232 cable and an ATE thatworked fine (the cable and the ATE) with a traditional desktop pc but not with a laptop.In the the end I discovered that the laptop sets the USB<->RS232 cable in suspend mode when not actively used,the desktop pc didn't.After disabling the suspend mode of the FTDI cable using an FTDI programming tool, the problem was resolved.

author: jonnyGURU
author_rank: Contributor
timestamp: September 10, 2021, 06:34:21 pm
content: Quote from: Karel on September 10, 2021, 06:30:32 pmHmm... You would think the ATE manufacturer would know that.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 10, 2021, 06:43:15 pm
content: Could it be that the ATE software is very old, and simply doesn't recognise COM ports that are connected via USB? A desktop PC with a COM port card would map them into address space differently to a modern laptop using a virtual COM port driver over USB.Do you get any clues from the software as to why it's not working? Does it say it can't find (say) COM1 at all? Or does it go through the motions but never actually transmit anything out on to the wire?What do you see if you put a scope on the Tx / Rx pins?

author: HKJ
author_rank: Super Contributor
timestamp: September 10, 2021, 06:48:04 pm
content: Problems may be related to the handshake signals, the voltage and the available current on a USB interface may not be the same as a native interface. It may even be that the PC software do not control the handshake signals correctly, assuming that the OS did the configuration.

author: nctnico
author_rank: Super Contributor
timestamp: September 10, 2021, 06:52:30 pm
content: I've also seen timing issues when using USB cables. Different USB-UART converter chips have different delays in their drivers. If the software expects an immediate response (within milli-seconds) then some USB cables might not work.

author: David Hess
author_rank: Super Contributor
timestamp: September 10, 2021, 07:35:21 pm
content: I have seen a lot of modern RS-232 devices which either use logic signal levels, which sometimes works, or even inverted signaling, which does not but has some justification if logic levels are used because all RS-232 transceivers are inverting.

author: nali
author_rank: Frequent Contributor
timestamp: September 10, 2021, 08:25:31 pm
content: Are you sure the USB adapter is working at all? Try a loopback test with a terminal program like puTTY (or better try 2 PCs talking to each other)What OS is the other old Compaq using? AndyC may have something about the software being old in which case it may be wanting to talk directly to the I/O and/or interrupts. If you're using a modern OS it'll not let you do that. If so, obtaining an add-in card won't really help you.

author: Bassman59
author_rank: Super Contributor
timestamp: September 10, 2021, 08:35:45 pm
content: Quote from: jonnyGURU on September 10, 2021, 06:34:21 pmThe ATE manufacturer gave you a solution that was known to work. They can't possibly test all of the various USB-to-RS232 converters, and we know that many of them are crap.So why should they know about a specific feature of a device they don't recommend?

author: thm_w
author_rank: Super Contributor
timestamp: September 10, 2021, 09:10:48 pm
content: Quote from: AndyC_772 on September 10, 2021, 06:43:15 pmThis is more likely, or a driver issue, especially if OP is using a quality USB-232 adapter, as in from a major brand. If they are using a cheap adapter, well, they deserve it.Typical things to check: COM port assigned to COM9 or lower (some apps don't like high numbers), program run in admin mode, compatibility mode (2000/XP), etc. Sometimes its easier to just dedicate an old PC to the task, as it is known to be working already on that compaq.

author: jonnyGURU
author_rank: Contributor
timestamp: September 10, 2021, 10:44:43 pm
content: Quote from: Bassman59 on September 10, 2021, 08:35:45 pmBecause surely they can't expect everyone that uses their ATE to have an old Pentium 4 Compaq laying around.New problem... I don't have any boards with PCI slots anymore! So that card isn't going to work any way.So apparently that particular RS232 card uses a Moschip MCS9865, which is a chip that uses ALL of the signals and apparently that's not a common thing for USB adapters. I did find this (with help):https://ftdichip.com/products/usb-com232-plus1/This also uses an IC with all of the signals. So barring any polling rate issues, it should work. If it doesn't, then I'm going to have to find a PCIe card.I have the new dongle coming in Tuesday. I'll let y'all know how it goes.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 11, 2021, 05:12:00 am
content: Uh, no mention of an OS? That’s not a minor detail. The ATE vendor does not specify which operating system is required? Which OS is the co-worker using that works? As mentioned, anything pre XP would probably only allow allow for COM 1 to 8, some old stuff only recognizes 1-4.PS: the cable tester is waste of time and money. No specs. It’s any ones guess as to what it considers a valid rs-232 level. It would just add to the confusion. Use a scope or don’t bother.

author: tkamiya
author_rank: Super Contributor
timestamp: September 11, 2021, 05:19:33 am
content: RS232C is always a big pain. Speed, parity, data length, start bit length, stop bit, and hand shake connection or override come into play. We now also have true RS232C voltage device and also lower voltage. Then TTL kind which has reverse logic. Sometimes, USB/Serial device can't sufficiently drive true 232C devices. I have several and I experience the same thing. Some combinations work, some do not.

author: David Hess
author_rank: Super Contributor
timestamp: September 11, 2021, 12:30:52 pm
content: Quote from: tkamiya on September 11, 2021, 05:19:33 amAnd the TTL kind *without* reversed logic.

author: jonnyGURU
author_rank: Contributor
timestamp: September 12, 2021, 06:39:54 pm
content: Quote from: WattsThat on September 11, 2021, 05:12:00 amOops. Sorry.The Compaq that works is running Windows XP.The manual for the software says Windows XP or 2000. So even if I have the correct hardware, I wonder if I would be able to get the software to work in compatibility mode.EDIT: They said Win 10 should be OK because they have customers that run their software in Win 10.However, they recommend using Win 7. Weird. I wonder why.

author: Zoli
author_rank: Frequent Contributor
timestamp: September 13, 2021, 12:48:29 am
content: Quote from: jonnyGURU on September 10, 2021, 10:44:43 pmI'm using a Rosewill RC-301EU for the last five years; it works flawlessly interfaced with a MAX3232(RPi connection).

author: jonnyGURU
author_rank: Contributor
timestamp: September 13, 2021, 02:57:30 am
content: I'm using a Rosewill RC-301EU for the last five years; it works flawlessly interfaced with a MAX3232(RPi connection).Are you using it with a SunMoon SM8800?

author: Zoli
author_rank: Frequent Contributor
timestamp: September 13, 2021, 03:31:24 am
content: Quote from: jonnyGURU on September 13, 2021, 02:57:30 amNo, I don't own SunMoon SM8800.Detailed explanation: the Rosewill card is fully featured RS232 card, with proper levels(I've measured the output: pin3 5.6V>5V(RS232 standard, IIRC)). On the other end of the cable is a MAX3232 to interface the Raspberry Pi 3, which has 3.3V CMOS levels; this is a permanent setup, since the remote access to Pi is disabled. On the cards other port I've tried AVRISP v1.0 and Edgerouter Lite; both worked flawlessly.Sidenote: older line receivers(DS1489) can be set up to switch only in negative range(see FIGURE 4, page 4 in the attachemnt), which can be PITA with the new converters.

author: nali
author_rank: Frequent Contributor
timestamp: September 13, 2021, 07:56:19 am
content: Quote from: jonnyGURU on September 12, 2021, 06:39:54 pmIf it helps, on the occasion I need to debug a serial connection I useDevice Monitoring Studio. It's not free software although the free version will allow you to do basic monitoring on COM ports. Also it works with USB adapters no problem.

author: bicycleguy
author_rank: Frequent Contributor
timestamp: September 13, 2021, 04:27:40 pm
content: There's this book 'The RS-232 Solution' by Joe Campbell, 1984, 194pages. I bought in 1988 for $16.95. The back cover says:Code:If you own a microcomputer, sooner of later you will need to connect "RS-232 compatible" equipment. Here, at last, is the book to show you how.You'll learn to connect your system to:printersmodemsterminalsplottersor any other RS-232 peripheral, using a simple fool-proof method that requires no expensive tools and only minimal knowledge of electronics. You won't even need the manufacturer's documentation!...Who could have known how prophetic this summary could be.. especially the last sentence. In the book the author explains how the RS-232-C 'standard' evolved into the cluster-f?ck it was in 1984 and I'm sure wouldn't be suprised to see where its at today.Amazon still sells the same edition paperback for $39.99.https://www.amazon.com/RS-232-solution-SYBEX-computer-books/dp/0895881403/ref=sr_1_1?dchild=1&keywords=the+rs232+Solution&qid=1631548621&s=books&sr=1-1

author: jonnyGURU
author_rank: Contributor
timestamp: September 16, 2021, 02:24:57 am
content: Well, turns out I got some good advice from an expert in the field. The USB adapter with the FTDI chip did indeed work like charm. And in Windows 10, no less.

author: xrunner
author_rank: Super Contributor
timestamp: September 16, 2021, 02:28:52 am
content: Quote from: bicycleguy on September 13, 2021, 04:27:40 pmI have that book in my bookcase!And guess what? I'm working right now on a project to read in NMEA sentences from my GPSDO coming over ... RS-232.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 16, 2021, 03:32:00 am
content: Quote from: jonnyGURU on September 16, 2021, 02:24:57 amIt’s not that it has an FTDI chip, it’s because it supports TX/RX plus the other handshake signals of DSR/DTR/RTS/CTS and perhaps even DCD and RI all at the proper RS-232 required voltage levels.If you’d tell us the brand and model of converter, we’ll know for the next time someone asks “which USB to RS-232 converter supports the old PC standard pin-outs and levels?”.I know from personal experience the Digi Edgeport brand of converters are 100% reliable for all applications but most wouldn’t want to pay for them as they run about $100 US.

author: gslick
author_rank: Frequent Contributor
timestamp: September 16, 2021, 05:07:50 am
content: Quote from: WattsThat on September 16, 2021, 03:32:00 amI have some Edgeport 4 and 8 port USB RS-232 devices from back when they were from Inside Out Networks, before they became Digi branded. The ones I have are implemented using old school traditional ST16C654 quad UARTs and MAX3243E RS-232 transceivers on the RS-232 interface side of the devices, with full support for all of the normal hardware handshake lines. I have never had any issues using these Edgeport devices all the way up through Windows 10 currently. If I had to replace them now I wouldn't want to pay the price for buying them new, but used eBay prices seem reasonable for devices that should just work reliably.

author: Karel
author_rank: Super Contributor
timestamp: September 16, 2021, 06:25:16 am
content: Quote from: jonnyGURU on September 16, 2021, 02:24:57 amI never use anything else than FTDI because so far I never had any issues on both Linux and windows.Never change a winning team.