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RS232 ansd RS485 — Parallax Forums

RS232 ansd RS485

pmartinpmartin Posts: 10
edited 2008-03-24 14:57 in Propeller 1
Hello,
I am designing a robot controller board and would like to use the Propeller chip as the controller. Has anyone had experience with hooking up a Prop chip to an external UART for RS485, or coding a RS485 driver?
Also, does anyone know the maximum baudrate of the FullDuplexSerial driver?

Thanks!

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-21 15:50
    Maximum Baud for the FullDuplexSerial driver is about 230KBaud, limited mostly because it has to be full duplex in one cog.

    RS485 is a hardware standard (do a Google search on "wiki RS485"). It's normally half-duplex, but can be set up as full duplex as well. A full duplex version could be used with FullDuplexSerial. The FullDuplexSerial driver could be modified fairly easily to accomodate a half duplex connection, but that has not been done.
  • lnielsenlnielsen Posts: 72
    edited 2008-03-21 17:57
    Which robot are you working with? There are two drivers that have been developed for the Bioloid (TTL/RS485 1 Mbps Half-duplex). You can drive the TTL bus with 2 resisters while the RS485 requires a MAX485 chip. I still intend to create my own driver for the Bioloid when I get some down time.

    Please tell us more about what you are trying to do.

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    BioProp: Robotics - Powered by Bioloids and controlled by the Propeller
  • pmartinpmartin Posts: 10
    edited 2008-03-22 12:53
    Oh very cool! I am using the Bioloid motors for a controlling a marionette! I have been a little unsatisfied with the Atmel chip in the stock CM5 controller, and I might want to add more features.
    Is this 485 driver in the object exchange?
  • StefanL38StefanL38 Posts: 2,292
    edited 2008-03-22 18:09
    Hello pmartin,

    yes the driver is in the object exchange. Again it's a standard serialdriver which you can combine with RS485, RS422, RS232
    because RS485, RS422, RS232 are only different HARDWARE-specifications. RS232 uses +-12V, RS422 uses +-5V
    RS485 uses +- CURRENT

    the fullduplex serialdriver is the LOGICAL Level ABOVE the hardwarelevel

    to make it even more clear you could connect interfaceadapters f.e. rs232 to RS485 then a RS485 to rs422 and then a RS422 to RS232 and everything will still work
    as long as both sides use the same LOGICAL protocol (with or without hardwarehandshaking, 3964R XON/OFF or what ever)

    the fullduplex serialdriver uses TX/RX without hardwarehandshaking
    you can adjust the parameters baudrate number of databits number of stopbits and paritybits


    regards

    Stefan

    Post Edited (StefanL38) : 3/22/2008 6:38:45 PM GMT
  • lnielsenlnielsen Posts: 72
    edited 2008-03-24 14:57
    pmartin,

    As Stefan said, TTL vs. RS485 is all hardware interfacing. We can do TTL with 2 resistors but RS485 requires an interface chip. The software driver is totally separate. A Bioloid specific driver is much better than using the generic full-duplex serial driver. There are links on two Bioloid forums on specific drivers for Bioloid packets using the Propeller. Read these threads for more information...

    http://robosavvy.com/forum/viewtopic.php?t=1056
    http://forum.crustcrawler.com/phpBB3/viewtopic.php?f=12&t=1050

    The threads are somewhat intertwined but in the end I think the community will have a well designed Bioloid object.

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    BioProp: Robotics - Powered by Bioloids and controlled by the Propeller
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