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Multi FTDI 232RQ — Parallax Forums

Multi FTDI 232RQ

DarrenYDarrenY Posts: 61
edited 2007-10-31 19:30 in Propeller 1
Hi Folks,

My design incorporates a 4 pin header for a prop plug for programming and debug, the prop plug RES pin is connected to the Prop RESn pin as per the prop demo schematic. Nice and simple.

I also want to have an on-board FT232RQ for PROP <--> HOST communications via a mini-USB connector. In theory I could operate them together, with debug data going out the prop-plug and program data out the mini-USB.

I'm not sure what I need to do with the onboard FT232RQ DTR pin in this instance - should I connect it as per the prop demo schematic to the Prop RESn pin? (so when both Prop plug and mini-USB connector are plugged in they both connect to the Prop's RESn pin)

This will be like having 2 prop-plugs connected to the system, with prop-plug#1 TX/RX going to pins30/31 and the second (on-board) prop-plug going to Pins X/Y.

Will this work OK?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-28 17:27
    You can ignore the 2nd DTR pin or connect it to an additional Prop I/O pin so your program can tell if there's a serial port on the other end of the USB connection. Don't connect it to RESn because your Prop will reset when the 2nd serial port is opened or closed (if you've got the capacitors on it).
  • DarrenYDarrenY Posts: 61
    edited 2007-10-28 19:39
    OK, thats what I was hoping but wanted to check.

    Can I connect the DTR pin direct to the Prop pin or should I keep the 10nF Cap, 10K Resistor and NPN inline as per the Prop demo schematic?
  • mynet43mynet43 Posts: 644
    edited 2007-10-28 19:53
    Related question. I'm also using the FT232RQ.

    Would someone please confirm that the prop reset line is internally pulled up. This doesn't seem to be covered in the Prop Data Sheet.

    In the Demo Board schematic, the reset pin seems to be used as a pull-up for the NPN transistor. Is this correct? It seems a little strange...

    Thanks for your help.

    Jim
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-28 19:56
    It is 100% sure internally pulled-up. This is officially documented, but have no inclination to search for that now.
    Nothing would work at all if it were not smilewinkgrin.gif
  • DarrenYDarrenY Posts: 61
    edited 2007-10-28 19:57
    Just answered my own question.

    The DTR output goes high (3.3v) when the mini-USB is connected, but yet the RES pin stays low (due to the components listed in the previous post)

    So I can connect the DTR direct and test for it going high to indicate that the FTDI is powered and ready for TX/RX
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-28 20:01
    The DTR will depend on the PC program running.
  • mynet43mynet43 Posts: 644
    edited 2007-10-28 20:11
    @deSilva,

    Thanks for confirming the reset is pulled high.

    It still seems very unusual for a reset pin to be used as a current source for other circuits. (e.g. Demo Board NPN)

    Do you know how much current it can source?

    Jim
  • mynet43mynet43 Posts: 644
    edited 2007-10-28 20:18
    I answered my own question. Reset depends on BOE. If BOE is pulled low (usually) then reset is a VDD output thru a 5K resistor, so it should be able to provide a little current.

    Jim
  • AribaAriba Posts: 2,686
    edited 2007-10-28 22:53
    @DarrenY

    How will you connect the 2 TX lines of the FT232RQ and the PropPlug together to the RX (Pin31) of the Propeller?
    You can not connect 2 outputs together without a appropriate circuit.

    Here is my suggestion:
    
FT232RQ   TX  &#61609;&#9472;&#9472;&#9472;&#9472;&#61629;&#61630;&#9472;&#9472;&#9472;&#9488;
                   4k7  &#9507;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#61627; RX Prop
                        &#9492;&#9472;&#9472;&#61606;&#61607;&#9472;&#9488;
Prop Plug TX  &#61609;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9496;



    Andy
  • DarrenYDarrenY Posts: 61
    edited 2007-10-29 09:10
    Hi Andy,

    I am going to connect the second FT232RQ to separate TX/RX prop pins so it won't be an issue but your right, if I were to use the same pin I would need a design like the one you describe.
    I need to TX/RX on both lines simultaneously, so I can't share the pins.
  • JavalinJavalin Posts: 892
    edited 2007-10-29 09:24
    Hello,

    Question for Mike Green -

    >(if you've got the capacitors on it).
    what capacitors??

    Also from my experience - the RES line is very weakly (100k?) pulled up.
    Additionally - there is supposed to be a IDE update to enable you to select the COMx: port to program - so you can have multiple PX8's on the PC.

    Cheers,

    James
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-29 14:00
    The capacitor(s) is the one in the DTR circuitry shown on the Propeller datasheet or on the Propeller diagrams websheet. It's used to turn the DTR edges into short reset pulse(s).

    DTR is normally taken true when a serial port is open and it's left true until the port is closed. The Propeller needs a short pulse on the leading edge of DTR. There's another pulse generated on the trailing edge of DTR, but it's the opposite polarity and dissipated in the protective diode in the Propeller's reset input.
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-30 00:14
    Reset is more complex... The DS 0.3 says:
    "Brown Out Enable (active low). Must be connected to either VDD or VSS. If low, RESn becomes a
    weak output (delivering VDD through 5 K&#937[noparse];)[/noparse] for monitoring purposes but can still be driven low to cause
    reset. If high, RESn is CMOS input with Schmitt Trigger."

    BOE is generally tied to GND (=Vss).
  • JavalinJavalin Posts: 892
    edited 2007-10-31 10:53
    Mike,

    (sorry - sorta hijacking this thread a bit but.....)

    Thanks for the reply - re the cap's.

    edit - sorry just re-read the post linked below - you've already commented.· Update to that post - have tried a .1uf cap to ground - works on the bread board I think - obv. cannot test it without the engine.· When it's on the pin and the serial programming circuit is connected you then cannot program the prop.· I'm ordering .01uf's caps to try.....

    I am running a propeller in a racing environment where the programming header (p30,p31,resn,gnd) has been available on the outside of the box either directly or via the serial programming circuit / max3232 (3.3v max232) driver.

    When the car (un-surpressed basic racing engine) rev's above about 3k then the prop just goes into reset, and reset, and reset etc. By my calculations 3k+ RPM is about 100htz+.

    Tried a pull up/pull down (cannot remember which way off hand) resistor and such to no avail.

    Only thing that works is to disconnect the RESn line from the outside world (then its contained within the metal box).

    Any thoughts?

    Many thanks.

    J

    (ps - also see http://forums.parallax.com/forums/default.aspx?f=25&p=1&m=185300#m185712 - for background)

    Post Edited (Javalin) : 10/31/2007 11:01:06 AM GMT
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-31 19:28
    Javelin, I read similar confusing posting in your April thread.
    It looks to me, as if you have not conected BOE to GND...
    The use of a cap between RES and GND is confusing as well...
  • JavalinJavalin Posts: 892
    edited 2007-10-31 19:30
    Hi deSilva,

    BOE definatly goes to VSS!

    The cap to ground was suggested in the previous thread as part of a low-pass filter. Idea being to absorb short spikes?

    J
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