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FTDI's UM232H for USB-to-RS-485 Serial Communications — Parallax Forums

FTDI's UM232H for USB-to-RS-485 Serial Communications

sunblocksunblock Posts: 55
edited 2014-10-10 22:56 in General Discussion
Greetings, everyone.

I received an email from a gentleman at Analog about FTDI's UM232H modules, and the ability of these modules to reach data rates of up to 16Mbaud...
having a half dozen of these little guys and a breadboard and am wanting to try to build a circuit.
The guy from FTDI, with his limited English said to simply:

[FONT=&#23435]Module1 J2 PIN6
Module2 J2 PIN6 [/FONT]
[FONT=&#23435]Module1 J2 PIN7
Module2 J2 PIN8[/FONT]
[FONT=&#23435]Module1 J2 PIN8
Module2 J2 PIN7[/FONT]

I've never used these devices, nor have I used or dabbled with serial communications at this level.
Since I rarely find anything is as easy as it seems, is it really as easy as connecting ground and cross-connecting send an receive to connect the UM232Hs together?
There is a programming tool to program the EEPROM on the UM232H to RS-485...

Has anyone any experience in this area?
Assuming the distance between the to UM232Hs is about 2" (inches), and they are drawing power from their respective USB buses, any other things I should do?

VR/JW--Sunblock

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-10-10 13:42
    sunblock wrote: »
    is it really as easy as connecting ground and cross-connecting send an receive to connect the UM232Hs together?

    I haven't used those particular RS-485 devices but I was under the assumption one only needed the two balanced wires for communication (and maybe a terminating resistor). I thought RS-485 did NOT require shared ground connections and I think I've read a shared ground connection with RS-485 could cause trouble.

    I have no idea why one would want RS-485 for two inches though. Is this just for testing?

    Do you have a link to these devices?
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-10-10 13:42
    FTDI has a USB to RS422/485 dongle that is extremely handy AT the computer to USB end--- nothing to solder. Once can just wire a socket of their choice to the end (either a DB-9 or RJ-45). But speed is restricted to 3Mbaud... more than enough for me. The Propeller or other device would just have RS422/485 tranciever chips, no USB. Distances can be extremely far.

    http://www.ftdichip.com/Products/Cables/USBRS485.htm

    I never looked at the modules you are referening to. They seem to be intended to do many more configurations and are not a completely enclosed solution. I suppose your choice depends on the particular project.

    Are you being WOWed by the 16Mbaud? I prefer to be WOWed by an easy to complete module that I can just get running quickly and apply to many projects. Do you have a computer that will handle the 16Mbaud. Tachyon Forth seems to have only gotten the Propeller 1 running up to 3Mbaud.

    +++++++++
    The RS422/RS485 dongle I mentioned can actually program a Propeller remotely over long distances as it has the additional control lines available for the required Reset. So it is just about all I could wish for in USB to RS422/RS485. The only reason I don't own one is that I built my own set up that does the same thing with a Parallax USB to Serial adapter.
  • sunblocksunblock Posts: 55
    edited 2014-10-10 16:05
    Duane Degn wrote: »
    I haven't used those particular RS-485 devices but I was under the assumption one only needed the two balanced wires for communication (and maybe a terminating resistor). I thought RS-485 did NOT require shared ground connections and I think I've read a shared ground connection with RS-485 could cause trouble.

    I have no idea why one would want RS-485 for two inches though. Is this just for testing?

    I thought I read that shared ground caused trouble too... but the FTDI guy confirmed his statement.
    Maybe I read it is a book or a short story by a guy named Axelson? Memory is getting flimsy

    The distance issue is keep the design small and try to push the limit of the 16Mbaud reliably.
    So I guess yes, for testing.
    Do you have a link to these devices?

    Here is the link to the datasheet.... there are many copies out there, but this one looks correct.
    http://www.ftdichip.com/Support/Docu.../DS_UM232H.pdf
  • sunblocksunblock Posts: 55
    edited 2014-10-10 16:09
    Are you being WOWed by the 16Mbaud? I prefer to be WOWed by an easy to complete module that I can just get running quickly and apply to many projects. Do you have a computer that will handle the 16Mbaud. Tachyon Forth seems to have only gotten the Propeller 1 running up to 3Mbaud.

    I know what you meant by asking if I was bin wowed by 16MBaud, and yes, actually that is the reason; and the fact that the UM232H is so configurable.
    In some configs supports >400Mbaud.

    I am only looking to connect the backside of these two devices together in an attempt to drive a non-stop 16MBaud stream.

    icon1.png Re: FTDI's UM232H for USB-to-RS-485 Serial Communications
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-10-10 19:38
    Chasing such high speed serial may just take you from one bottleneck to another. You may well find that you can't buy or build a 16Mbaud (if it is really Megabaud, not Megabit) cable, much less something faster. And even if you to get the USB cable right, there is the problem of what your USB drivers, PC hardware, and OS system might throw at you.

    The prime advantage that RS422/RS485 offers is clean fast asynchronous serial over long distances of wire.

    The prime advantage of USB is one plug fits everything over short distances.

    If I wanted a PC to get the most out of RS422/RS485, I would install a card on the mother board intended just for that not have the USB involved in anyway.

    And so, I can't quite see what advantage the device you are interested in really is going to offer.
  • kwinnkwinn Posts: 8,697
    edited 2014-10-10 20:13
    sunblock wrote: »
    Greetings, everyone.

    I received an email from a gentleman at Analog about FTDI's UM232H modules, and the ability of these modules to reach data rates of up to 16Mbaud...
    having a half dozen of these little guys and a breadboard and am wanting to try to build a circuit.
    The guy from FTDI, with his limited English said to simply:

    [FONT=宋]Module1 J2 PIN6
    Module2 J2 PIN6 [/FONT]
    [FONT=宋]Module1 J2 PIN7
    Module2 J2 PIN8[/FONT]
    [FONT=宋]Module1 J2 PIN8
    Module2 J2 PIN7[/FONT]

    I've never used these devices, nor have I used or dabbled with serial communications at this level.
    Since I rarely find anything is as easy as it seems, is it really as easy as connecting ground and cross-connecting send an receive to connect the UM232Hs together?
    There is a programming tool to program the EEPROM on the UM232H to RS-485...

    Has anyone any experience in this area?
    Assuming the distance between the to UM232Hs is about 2" (inches), and they are drawing power from their respective USB buses, any other things I should do?

    VR/JW--Sunblock

    I have not used this chip, but based on what I have read in the data sheet it should be as simple as wiring it up as you posted provided the two modules are only a few inches apart. As far as software and setup, I have not had time to study that closely.

    If you want to use RS232/422/485 you will need to add the appropriate driver chips for that. Signals out from the module are logic level. Looks to me like this module was intended to allow a PC with high speed USB ports to interface to high speed serial networks or to communicate with microcontrollers that have high speed serial interfaces like spi, i2c, and asynch, etc.
  • sunblocksunblock Posts: 55
    edited 2014-10-10 20:32
    kwinn wrote: »
    I have not used this chip, but based on what I have read in the data sheet it should be as simple as wiring it up as you posted provided the two modules are only a few inches apart. As far as software and setup, I have not had time to study that closely.

    If you want to use RS232/422/485 you will need to add the appropriate driver chips for that. Signals out from the module are logic level. Looks to me like this module was intended to allow a PC with high speed USB ports to interface to high speed serial networks or to communicate with microcontrollers that have high speed serial interfaces like spi, i2c, and asynch, etc.

    Yes, I realized at some point into a couple of shots of Tullamore Dew Irish Whiskey that the output was TTL level.
    I am now looking for a couple of development, mini-boards that could provide the TTL to RS-485 level conversion to put between the two UM232Hs.

    Do you have a suggestion of any devices/mfg that might be better than others?
  • kwinnkwinn Posts: 8,697
    edited 2014-10-10 21:04
    sunblock wrote: »
    Yes, I realized at some point into a couple of shots of Tullamore Dew Irish Whiskey that the output was TTL level.
    I am now looking for a couple of development, mini-boards that could provide the TTL to RS-485 level conversion to put between the two UM232Hs.

    Do you have a suggestion of any devices/mfg that might be better than others?

    Sorry, I am still using up my stock of 75176 chips since most of my work is in automation systems that rarely go over 38.4Kb/sec. You could take a look at this forum thread "http://forums.parallax.com/showthread.php/157730-Propeller-networking". There was some mention of RS485 drivers in there.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-10-10 22:14
    The 75176 is a very adequate RS422/485 transceiver, but if you want more in performance Maxim has a wide array of specialty choices.

    While I think that 3Mbaud is still possible, (The FTDI dongle I mentioned claims 3Mb limit with true RS422/485), I suspect that is about the limit for RS422/485. 16Mbaud might have referred to USB to parallel i/o at the TTL level. But I do see a lot of material that limits RS422/485 to 115200 baud with certain common driver chips. The Propeller has also be demonstrated with direct USB to USB at 3Mbaud, but not beyond that.

    http://www.maximintegrated.com/en/products/interface/transceivers/rs-485-rs-422-transceivers.html

    I don't think you need a board as the majority of these chips are available in 8 pin DIP. But EBay and Sparkfun both have boards. Sparkfun's RS485 is half-duplex only at 10Mbps limited.

    http://www.ebay.com/itm/RS485-Board-5V-MAX485-RS-485-Transceiver-Converter-Evaluation-Development-Kit-/251042731970

    Frankly, anything above 115200 baud is something I generally avoid.

    Maxim seems to have one that is documented as 'high speed' at 40Mbps (bits per second) or roughly something less than 5Mbytes/sec (I estimate about 4.44Mbytes/sec)

    http://www.maximintegrated.com/en/datasheet/index.mvp/id/4073
  • jmgjmg Posts: 15,173
    edited 2014-10-10 22:50
    sunblock wrote: »
    I am only looking to connect the backside of these two devices together in an attempt to drive a non-stop 16MBaud stream.

    ? Where did the 16MBaud come from ?
    The FT232H data claims only 12MBaud Serial ?

    There are a few tests you can do, that I used to test Terminal Software
    a) Send only, transmit 'U' continually and use a Freq Counter to verify 6.000MHz on the TXD ( @ 12MBd = no Gaps send)
    b) Self Loopback, by connect RX to TX, and confirm a) speed
    Count chars sent/Rx, to verify no dropped chars
    c) Paired loopback, one device TX to another's RX
    d) Test also FT2232H - that part is also High Speed, but it has larger on chip buffers

    We found the FT2232H would sustain higher continual data rates, than FT232H, because of those larger buffers.

    Some care is needed in the PC software to keep the packet size up, to achieve sustained speeds.
    PC software starts to matter more at higher speeds.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-10-10 22:56
    Here is a quote from the FT232H document. 40Mbytes/second is synchronous parallel.

    I knew this didn't make sense with RS485. The driver chips just won't go faster than 40Mbps.

    "Data Transfer rate. The FT232H supports a data transfer rate up to 12 Mbaud when configured as an
    RS232/RS422/RS485 UART interface or up to 40 Mbytes/second over a synchronous 245 parallel FIFO
    interface or up to 8 Mbyte/Sec over an asynchronous 245 FIFO interface."
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