[SOLVED !] PDS Bootloader:is max232 really necessary?


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Thread: PDS Bootloader:is max232 really necessary?5515 days old

  1. #1
    donomark
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    Question PDS Bootloader:is max232 really necessary?

    As PDS and proton board user I have found that the boot loader is quite useful. I have used it many times without problems.
    Now I want to create a board for a project and I would like to use the bootloader for pic programming (so without adding the connector for ICSP socket for Epic. I download the bootloader sw via ziff socket on my ICSP programmer).
    I would like to know it the voltage level translator Max232 (or equivalent) are really needed for reading/writing to pic with bootloader. For normal serial communication between pic and PC I have used many and many time (thanks also to the excellent pic hardware) a serial cable with only two resistors.
    Because I'll use the serial port only for programming (not a very ripetitive task) I would like to avoid the max232 (not for the cost but for board space).

    Do you think Is it possible?

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  3. #2
    Maverick
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    The harware Uart is TTL232 and therefore not only are the Voltage levels different from true RS232, but the signals are also inverted. The MAX232 not only converts +12-12v to 5v and 0v respectivley but also inverts the signal in the process making it compatible with the hardware Uart.
    There are alternatives to the MAX232 ,, Take a look at the dallas chip DS275 , this is an 8pin chip and requires no external components.

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  5. #3
    donomark
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    Maverick,

    thank you for your answer. The DS275 is interesting but in the schematich on page 27 revision 1.2 of the PDS manual I see that 3 serial line are used (one is for the MCLR). It seems to me that the proton board does not have the MCLR connection to RS232. If this is true and so the MCLR pin is not so necessary for bootloader (I think it could be used for automatic pic reset before programming/reading) I'll surely try the DS275.

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  7. #4
    bruce
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    The Mecanique boot-loader software toggles the PC DTR output pin to reset the PIC at the start of the boot-load process.

    If you build the circuit shown in the Proton manual, the loader process is hands-free. If not, then you'll need to manually reset PIC.

    The loader uses the USART, so you either need a max232 type IC or an equivalent circuit constructed from discreet components. You can build a similar circuit using transistors. Take a look at the schematics for a BASIC Stamp II module on the Parallax website for a simple circuit used to replace a max232 IC.

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