RS-232 confusion


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  1. #1
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    Default RS-232 confusion

    This may be a case of a dog chasing his own tail but I'm trying to figure out if what I'm looking at is an RS-232 signal. I've tried various baud rates and it seems to be something around 9600 as that's the most consistent data I can see on the screen. Each piece of data is 500uS. If it's not RS-232, can anyone identify the communication protocol?Name:  IMG_2011 copy.jpg
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  2. #2
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    Default Re: RS-232 confusion

    definitely not rs232 and not a Manchester code , its a rtz(return to zero) stream of some sort . where does it come from and is there any identifiable start/stop sequence


    bi-phase ?

  3. #3
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    Default Re: RS-232 confusion

    Also, RS-232 signals go from -12V to +12V. What you have there is some kind of 1-wire serial communication going on.
    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  4. #4
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    Default Re: RS-232 confusion

    It is one wire communication. The voltage level is 18VDC. What you see in that picture the output from a RS-232 IC. I can identify the start/stop and know what each piece of data is. The problem is, I have to do it with my oscilloscope and eyes as opposed to using a PIC to interpret it.

    Each bit is 500uS. The high/low within the 500uS bit is predetermined. In other words, it may be 200uS off and 300uS on or 400uS on and 100uS off but I know before the packets starts. The entire packet is 100mS long.

    What is the best way to get this information to a PIC where I can log it instead of staring at my oscilloscope?

  5. #5
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    Default Re: RS-232 confusion

    if you can't identify the device then a complete transaction from line idle to send/receive and back to idle with a data translation would help . guessing seems pointless

  6. #6
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    Default Re: RS-232 confusion

    If you know it's RS232, why not send into a PC?

    Assuming you don't have a Saleae logic probe or other device capable of reading signal.

    Robert

  7. #7
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    Default Re: RS-232 confusion

    If you know it's RS232, why not send into a PC?
    Richard has confirmed it's not RS-232.
    definitely not rs232
    if you can't identify the device then a complete transaction from line idle to send/receive and back to idle with a data translation would help . guessing seems pointless
    I can identify everything.

    I don't really need to convert the data into a "readable" format, all I need to do is accurately measure the on/off period in each bit. For example, if I'm able to do something like this, my job is complete:

    Bit 1 // On - 100uS / Off - 400uS
    Bit 2 // On - 350uS / Off - 150uS
    Bit 3 // On - 100uS / Off - 400uS
    Bit 100..........

    I'm using an 18F87J50 and tried using an ECCP input but was never able to get it working. Then I figured if it was some type of standard communication I'd be able to push the easy button but that's not a reality now.

  8. #8
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    Default Re: RS-232 confusion

    I got confused by this I guess.
    What you see in that picture the output from a RS-232 IC
    If you only want to know ON/OFF duration of 18v signal, why not use the signal to control the base of a transistor that would send 5v to a PIC?

    Then I would use interrupts on that pin and use a timer.

    Robert
    Last edited by Demon; - 17th March 2015 at 01:12. Reason: corrected Gate to Base

  9. #9
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    Default Re: RS-232 confusion

    getting info here is a bit like pulling teeth , but lets assume a 48mhz clock and that timer4 is free along with a pin like portb .2
    Code:
    some vars
    bit_is var byte 
    I_data var PORTB.2    'lets call this the input
    
    a routine
    bit_test:
    bit_is =0
    t4con=0   ' timer off
    tmr4=0   ' clear timer 
    pir3.3=0  'clear timer overflow flag
    
    while ( ! i_data) : wend 'wait here till input goes high  to sync up
     while ( i_data) : wend  ' wait here till input goes low
    t4con=6     ;  prescale 16 timer on
     while ( ! i_data) : wend  ' wait here till input goes high  
     if  pir3.3 then bit_is=1  ;  offtime > 340 uS  
    else
      bit_is=0 '  the offtime < 340 uS 
    
    endif
           
     return
    it could be nicer if
    1 does the line idle high or low
    2 what does a start bit look like
    3 how many bits in a session
    4 100uS / Off - 400uS a 1 or a 0 ?

  10. #10
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    Default Re: RS-232 confusion

    If you only want to know ON/OFF duration of 18v signal, why not use the signal to control the base of a transistor that would send 5v to a PIC?

    Then I would use interrupts on that pin and use a timer.
    I'm a novice when it comes to the timers and interrupts. Seems like a good idea that's worth trying.

    1 does the line idle high or low
    Idles low.

    2 what does a start bit look like
    1ms on/1ms off

    3 how many bits in a session
    100

    4 100uS / Off - 400uS a 1 or a 0 ?
    It's a 1 but it can vary. Before the packet is received, I will know what is a 0 and what is a 1.

  11. #11
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    Default Re: RS-232 confusion

    this should get close to it


    Code:
    define OSC 48
    some vars
    bits var byte[13] ' an array to hold the 100 bits
    I_data var PORTB.2    'lets call this the input
    bit_count var byte
     
     
    'a subroutine
    bit_read:
    t4con=0   ' timer off
    tmr4=0   ' clear timer
    bit_count = 0
    while ( i_data) : wend  ' wait here till input goes idle
    while ( ! i_data) : wend 'wait here till input goes high  to sync up
    t4con=$7e  '256:1// count of 45 or so = 1mS
    while ( i_data) : wend  ' wait here till input goes low
    t4con=0   ' timer off
    if (tmr4 >43 ) and (tmr4 < 47) then goto start_ok '  bit of latitude might need more
    goto bit_read
    start_ok:
    while bit_count < 100
    tmr4=0   ' clear timer 
    pir3.3=0  'clear timer overflow flag
    while ( ! i_data) : wend 'wait here till input goes high 
    t4con=6     ;  prescale 16 timer on
    while ( i_data) : wend  ' wait here till input goes low
    t4con=0   ' timer off
     if  pir3.3 then bits.0[bit_count]=1  ;  ontime > 340 uS  
    else
      bits.0[bit_count]=0 '  the ontime < 340 uS 
    endif
     bit_count=bit_count+1
    wend
           
     return

  12. #12
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    Default Re: RS-232 confusion

    As far as the IDLE high or IDLE low state, looking at the signal with a scope, where is the bus signal level when NO data is being sent? I would imagine it to be high, as most single wire communications use a passive sourced current to stimulate the bus wire (usually a resistor). That way there can be more than 1 device listening as well as more than 1 device able to answer a request. This is done by pulling the line LOW thru an open collector transistor or N channel fet.
    Dave Purola,
    N8NTA
    EN82fn

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