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Moving from Prop Pro Dec board to stand-alone — Parallax Forums

Moving from Prop Pro Dec board to stand-alone

TimHTimH Posts: 48
edited 2009-11-23 14:45 in Propeller 1
Hello

I have 99% finished developing a simple project using the Propeller Professional Development board and I now want to move it over to a printed circuit board.
I have looked at the circuit diagram for the dev board (page 17 in the propeller manual) and also the schematic for the propeller demo board and my question is are there any other things I should be concerned about when designing the pcb other than the EEPROM, Crystal and power supply.
I assume I can load the software into the EEPROM using the Prop Pro development board and then move it into the socket on the pcb.
Can I use a standard (5V) MAX232 and add inline resistors between the MAX232 and Propeller or should I go with a 3.3 version of the MAX 232.

Thanks for any help

Tim

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-11-22 23:17
    Use a MAX3232 which runs off 3.3V.
  • TimHTimH Posts: 48
    edited 2009-11-23 00:07
    Mike

    Given that I will have 5V on the board and also that I have quite a few of the standard (5V) Max232 on hand is there any other reason to use the 3.3 version.
    Also I noticed on both schematics that there are no caps from the crystal to gnd as is common on many processors.

    Tim
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-11-23 00:42
    A max232 is fine if you have lots of them. Just add two 1k resistors - one between pin 12 max232 and the prop, and the other between pin 9 and the prop.

    No caps are needed on the xtal.

    You can program it all sorts of ways - certainly you can move the eeprom physically from one board to the other. However, it might get a bit tedious if you are doing lots of changes. There are many solutions and it partly depends if you have USB or a real serial port on your PC, but I went for a standard D9 female socket on the board.

    If you are drawing up a PCB, maybe post the schematic and board here before sending it off to be made.

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    www.smarthome.viviti.com/build
  • TubularTubular Posts: 4,717
    edited 2009-11-23 00:47
    Hi Tim,

    I was initially thinking the same as Mike - MAX3232. There are other nice things about the MAX3232 - it works off 5v or 3v3, and the caps are smaller 100nF instead of 1uF. But since you have lots of MAX232's you may as well use those with the interface resistors in between the prop.

    You can certainly do as you suggest - program the prom and transfer it across. Don't forget to pull up at least the SDA like to the eeprom on your board, and tie the 3 address pins low.

    Other than that, general common sense PCB layout applies - bypass caps near the prop pins, keep crystal runs as short as practical, run your power radially back to the regulated source, and you should be fine. I'm assuming you're going the DIP path - if you're going SMT there are advisories for best practice power plane layout (to minimize potential PLL failures), capacitors (for overclocking)

    The crystals don't need the two ground connected caps for Prop use. As per the manual page 15 "Crystal Input. Can be connected to output of crystal/oscillator pack (with XO left disconnected), or to one leg of crystal (with XO connected to other leg of crystal or resonator) depending on CLK Register settings. No external resistors or capacitors are required."

    have fun
    tubular
  • LeonLeon Posts: 7,620
    edited 2009-11-23 00:49
    The Propeller includes the oscillator feedback capacitors.

    Leon

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    Amateur radio callsign: G1HSM
  • TimHTimH Posts: 48
    edited 2009-11-23 01:27
    Thanks for the good advise everyone.

    Tim
  • DroneDrone Posts: 433
    edited 2009-11-23 14:24
    Hi Tim,

    I'm not sure if you intend your MAX232 to act as a serial programmer or just to break out a new serial port. You can use the likes of a PropPlug or a discrete serial programing interface as a general purpose serial interface also. The Propeller Serial Terminal available for download from the Parallax Web site is a good example of this. There is a discrete serial interface programming circuit shown on the Propeller Data Sheet (latest as of writing time is V1.2). If you want the MAX232 to act as a serial programming interface you will need to bring forth the DTR reset as well. If you just want to use the circuit as a separate serial interface you can drop the parts associated with the DTR reset portion. There is a "two resistor" non programming serial interface that may work OK for you on the Propeller Wiki. See here: propeller.wikispaces.com/Two-Resistor+Serial+Interface.

    There was a post here recently about someone wanting to add a section to the Propeller Wiki with tips on building your own Propeller board. Can't find it right-off though. Also, I did see a recent thread about someone having problems with leaving BOEn pin floating (as in the Propeller ProtoBoard schematic V1.3) in noisy environments; if memory serves (it often doesn't these days) it was suggested to add a bypass cap to BOEn.

    Regards, David
  • TimHTimH Posts: 48
    edited 2009-11-23 14:45
    Hi David

    No the MAX232(2) will be used only as a general purpose RS232 port not to program the Prop. As I don't expect mass production I will use the Propeller Pro development board to load the EEPROM which I will then plug into the pcb. Thanks for the warning about BOEn

    Tim
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