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Serial port connection — Parallax Forums

Serial port connection

ambroxioambroxio Posts: 17
edited 2012-01-31 01:38 in Propeller 1
Hello. I just received my first propeller chips :-D ... I wasnt able to buy the propplug so I am going to set up a serial port connection circuit.

My question is, has anyone here used this before and would you recommend the schematic in the datasheet (which is quite simple, a pair of transistors, a few resistors and a cap) or this one http://www.extremecircuits.net/2010/06/programming-propeller-ic_17.html

I guess both work, but which is better and is there some hint you could give so I dont have any problems with it . thanks

Comments

  • ambroxioambroxio Posts: 17
    edited 2010-12-30 23:25
    just found this http://forums.parallax.com/showthread.php?113577-Serial-Port-connection
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-12-31 00:09
    I use the three transistor version for most of my circuits.

    I made up a separate PCB that goes to a 5 way header socket, this allows for the extra (fifth) connection for the 3.3 Volts from the Prop board to power the interface. It is great not having to build the same bit of circuit over and over again. I put a jumper link into the RESET output line just in case this gets toggles by the PC when serial comms is being done. There has been a discussion about the use of a PNP transistor instead of the NPN one on the reset line, but the usuall NPN (as in the diagrams) gives no problems.

    Using a MAX3232 chip does give true '232 voltages, which the transistor interface does not. It all depends what the interface will get used for.
  • AribaAriba Posts: 2,690
    edited 2010-12-31 00:34
    My hint:
    Don't connect the 4.7k resistor for the RX line to DTR but to Ground (red line in the attached schematic). Otherwise you are ony able to program the Propeller, but not to communicate with a Terminal or other PC applications (because they have the DTR line normally in the wrong state).

    Andy
    SerialConnection.JPG
    645 x 378 - 22K
  • ambroxioambroxio Posts: 17
    edited 2011-01-03 15:48
    I have built the 3 transistor schematic. I'll test it tomorrow when I get the 3.3 volt regulator. Thanks for the advices.

    BTW . Im having trouble finding a 78L33, is it ok to do the regulation with a zener diode or is it ok with a 3volts regulator ¿
  • StefanL38StefanL38 Posts: 2,292
    edited 2011-01-03 15:55
    the voltage-range of the propeller-chip is 2.7V-3.6V so a 3V will do.
    Depending on the current you want to pull out of IO-pins the zener-diode and the current-limiting resistor have to be pretty big

    a 7833 would be a 33V-regulatot not a 3.3V

    you can get them from parallax
    http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/473/Default.aspx?txtSearch=3.3V+regulator


    best regards

    Stefan
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-01-03 18:01
    ambroxio: Firstly, welcome to the prop forum. We are a friendly buch with lots of help to give. Any questions will get lots of answers.

    Easiest to use a 3V3 regulator. Just be careful with the pinout as some regulators use different pinouts. You will also need a cap on the input and output pins of the regulator so see the relevant regulator specs for values.
  • ambroxioambroxio Posts: 17
    edited 2011-01-03 21:07
    78L33 != 7833 :p

    anyway i just remembered i could use a lm317 with two resistors
  • ambroxioambroxio Posts: 17
    edited 2011-01-03 21:08
    thanks for the welcome Cluso99 :)
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-01-04 01:06
    Brilliant idea with the LM317. Use what parts you have to hand. My first Propeller ran off a 7805 with three 4001 diodes for voltage drop. Then I bought some 3.3V regulators, and more recently I got some 3.3V switching regs http://www.futurlec.com/Linear/LM2574HVN.shtml $1.70 plus about $2 for the inductor. No heatsink needed.

    Welcome also to the forum. We are a very friendly bunch. I can recount a personal story here - Cluso99 lives several thousand kilometres from me but he once flew over to my city as he was visiting family and came to visit and personally helped solve a number of problems I had with the Propeller chip. You don't get more friendly than that!
  • ambroxioambroxio Posts: 17
    edited 2011-01-04 21:33
    thanks dr_acula !

    well I am testing the circuit right now and the propeller tool isnt finding the chip :S .. I have the 3.3 volt power supply, the 3transistor circuit and the prop with a crystal and a eeprom ... what should I test first to get to the problem ¿¿
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-04 21:51
    The Prop doesn't need the crystal or the EEPROM for the Prop Tool to find it. It needs power and a serial connection. Make sure the 3-transistor interface circuit is wired correctly and make sure the Propeller and the interface circuit is receiving 3.3V. Make sure the grounds are connected properly as well.

    If you're using a direct serial connection to your PC's serial port, make sure the cable is wired correctly. If you're using a USB to serial adapter, remember that many of these adapters don't implement DTR correctly and won't work with the Propeller Tool. You can't use the default Windows USB driver and have to use the driver for the specific adapter.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-01-04 21:53
    Since you said in your first post that you had just received your propeller chips, I presume you are breadboarding your prop setup. Perhaps you could post some photos so we can see what you have setup.
    The xtal is not used to find the prop or download, so that will not be the problem.
    The eeprom is not required to find the prop or download, so that will not be the problem either.
    Therefore, the prop circuit can be extremely basic to get running.

    Have you connected both sets of power and ground pins of the prop? And do you have capacitors across them?
    Have you connected BOE to Gnd?
  • ambroxioambroxio Posts: 17
    edited 2011-01-04 22:07
    ok i got rid of the eeprom and the crystal .

    The prop tool found it now . I think maybe something of that was bad wired thanks for the help I'll play a little with the thing now :D
  • ambroxioambroxio Posts: 17
    edited 2011-01-05 09:56
    I first connected the crystal, and now I connected the eeprom, but if I try to load the eeprom with the prop tool it says "eeprom verify error" . I saw lots of threads about this in the forum but all people got was [contact parallax support] . but I am not able to make long distance calls and if the chip is damaged I would buy a new one instead of getting a replacement from parallax for shipping prices

    I am gonna try BST later though . maybe its a prop tool or a windows issue
  • ambroxioambroxio Posts: 17
    edited 2011-01-05 10:43
    BST says eeprom verify error too :S
  • SapiehaSapieha Posts: 2,964
    edited 2011-01-05 11:00
    Hi ambroxio.

    That give me thinking that You maybe have BAD EEProm (Propeller need at last 32KBytes EEProm).




    ambroxio wrote: »
    BST says eeprom verify error too :S
  • ambroxioambroxio Posts: 17
    edited 2011-01-05 11:15
    thanks sapieha .

    I just watched the datasheet of my eprom and i didnt notice it isnt 32Kbytes but 32Kbits -____-

    thanks for the help
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-01-05 15:18
    ambroxio: You need an AT24C256 (256kbits=32KB) or AT24C512 (64KB) or equivalent. Not all I2C eeproms are equivalent. The 64KB is usually not much more expensive than the 32KB so we often use these as we can store other things in the upper 64KB sometimes. The AT24C1024 is usually quite a bit more expensive so not used often. AT=Atmel.
  • rook128rook128 Posts: 8
    edited 2012-01-31 01:38
    i have also put together the diagram using the 3 transistors. however, the prop tool doesnt detect my propeller. i checked the voltage levels on the circuit and heres what i got.
    TX -5.62V
    RX -1.92V
    DTR -5.61V

    RESn of the propeller is getting 0Volts...

    can these voltage levels be causing the problem? what sholud i do? should i try implement the circuit with 2 transistors?
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