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serrial ADC shiftin/shiftout problems — Parallax Forums

serrial ADC shiftin/shiftout problems

ArchiverArchiver Posts: 46,084
edited 2003-06-21 22:00 in General Discussion
Hello again!

I'm attempting to interface an LTC1298CN8 12-bit serial ADC converter to a
BS2. For a test, I simply have a 50k pot as a voltage divider from +5 to
ground, with the slider attached to the + input of the ADC. PIN0 is my CLK
pin, PIN1 is Dout, PIN2 is Din, and PIN15 is !CS on my stamp. I read the
data into variables called SampleLow and SampleHigh, then debug them to the
PC. The code is below. I always get a result of "0:0", so the variables do
not seem to be getting chnaged during the SHIFTIN function.

Any ideas?

Steve


'{$STAMP BS2}
'{$PBASIC 2.5}

SampleLow VAR byte
SampleHigh VAR Byte

DEBUG "Startup", Cr
high 15
PAUSE 1000
DEBUG "Entering Main", cr
Main:
LOW 15
SHIFTOUT OUT1, OUT0, LSBFIRST, [noparse][[/noparse]%00011\4]
SHIFTIN IN2, OUT0, LSBFIRST, [noparse][[/noparse]SampleLow\8, SampleHigh\4]
HIGH 15
DEBUG DEC SampleHigh, ":", DEC SampleLow, CR
PAUSE 5
GOTO Main
end

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-06-21 19:59
    Hi Steve,

    You probably need this:

    SHIFTOUT 1, 0, LSBFIRST, [noparse][[/noparse]%00011\4]
    SHIFTIN 2, 0, LSBFIRST, [noparse][[/noparse]Sample\12]

    Look at what you have:

    > SHIFTOUT OUT1, OUT0, LSBFIRST, [noparse][[/noparse]%00011\4]
    > SHIFTIN IN2, OUT0, LSBFIRST, [noparse][[/noparse]SampleLow\8, SampleHigh\4]

    What happens? SHIFTIN reads the value (0 or 1) currently present on
    p2 and uses that as the data pin, and it reads the state of the OUT0
    register( 0 or 1) and uses that value as the clock pin. Not what you
    want!

    In PBASIC 2.5 there is a new variable type:


    '{$PBASIC 2.5}
    LT1298do pin 2
    LT1298di pin 1
    LT1298ck pin 0

    The interpreter figures out from context whether it needs to be used
    directly as a constant or indirectly as a variable.

    LT1298ck=0 ' sets (out0=0)
    input LT1298do ' makes p2 an input (input 2)
    debug ? LT1298di ' shows the current status of p1 (debug ? in1)
    SHIFTIN LT1298do, LT1298ck, LSBfirst, [noparse][[/noparse]sample\12} ' old way
    SHIFTIN 2,0,...

    In the first and third cases, the compiler substitutes the reference
    to a variable into the tokenized code, but in the second and fourth
    cases, it subs the constant values. It used to be that you would
    have to define two things, for example, you might have to define both
    a constant and a variable:

    pin_as_constant con 2
    pin_as_variable in2 ' reference as variable
    if pin_as_variable=0 then skipaction ' reference as constant
    pulsout 2, 1000
    skipaction:

    Now it can be one thing:

    what_a_pin pin 2
    if what_a_pin=0 then pulseout what_a_pin,1000
    ' the compiler sorts it out!

    -- regards,
    Tracy Allen
    electronically monitored ecosystems
    mailto:tracy@e...
    http://www.emesystems.com




    >Hello again!
    >
    >I'm attempting to interface an LTC1298CN8 12-bit serial ADC converter to a
    >BS2. For a test, I simply have a 50k pot as a voltage divider from +5 to
    >ground, with the slider attached to the + input of the ADC. PIN0 is my CLK
    >pin, PIN1 is Dout, PIN2 is Din, and PIN15 is !CS on my stamp. I read the
    >data into variables called SampleLow and SampleHigh, then debug them to the
    >PC. The code is below. I always get a result of "0:0", so the variables do
    >not seem to be getting chnaged during the SHIFTIN function.
    >
    >Any ideas?
    >
    >Steve
    >
    >
    >'{$STAMP BS2}
    >'{$PBASIC 2.5}
    >
    >SampleLow VAR byte
    >SampleHigh VAR Byte
    >
    >DEBUG "Startup", Cr
    >high 15
    >PAUSE 1000
    >DEBUG "Entering Main", cr
    >Main:
    > LOW 15
    > SHIFTOUT OUT1, OUT0, LSBFIRST, [noparse][[/noparse]%00011\4]
    > SHIFTIN IN2, OUT0, LSBFIRST, [noparse][[/noparse]SampleLow\8, SampleHigh\4]
    > HIGH 15
    > DEBUG DEC SampleHigh, ":", DEC SampleLow, CR
    > PAUSE 5
    >GOTO Main
    >end
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-21 22:00
    Perfect!

    I made these simple changes, and it works flawlessly!

    Thank you!

    Steve
    Original Message
    From: "Tracy Allen" <tracy@e...>
    To: <basicstamps@yahoogroups.com>
    Sent: Saturday, June 21, 2003 8:59 PM
    Subject: Re: [noparse][[/noparse]basicstamps] serrial ADC shiftin/shiftout problems


    > Hi Steve,
    >
    > You probably need this:
    >
    > SHIFTOUT 1, 0, LSBFIRST, [noparse][[/noparse]%00011\4]
    > SHIFTIN 2, 0, LSBFIRST, [noparse][[/noparse]Sample\12]
    >
    > Look at what you have:
    >
    > > SHIFTOUT OUT1, OUT0, LSBFIRST, [noparse][[/noparse]%00011\4]
    > > SHIFTIN IN2, OUT0, LSBFIRST, [noparse][[/noparse]SampleLow\8, SampleHigh\4]
    >
    > What happens? SHIFTIN reads the value (0 or 1) currently present on
    > p2 and uses that as the data pin, and it reads the state of the OUT0
    > register( 0 or 1) and uses that value as the clock pin. Not what you
    > want!
    >
    > In PBASIC 2.5 there is a new variable type:
    >
    >
    > '{$PBASIC 2.5}
    > LT1298do pin 2
    > LT1298di pin 1
    > LT1298ck pin 0
    >
    > The interpreter figures out from context whether it needs to be used
    > directly as a constant or indirectly as a variable.
    >
    > LT1298ck=0 ' sets (out0=0)
    > input LT1298do ' makes p2 an input (input 2)
    > debug ? LT1298di ' shows the current status of p1 (debug ? in1)
    > SHIFTIN LT1298do, LT1298ck, LSBfirst, [noparse][[/noparse]sample\12} ' old way
    > SHIFTIN 2,0,...
    >
    > In the first and third cases, the compiler substitutes the reference
    > to a variable into the tokenized code, but in the second and fourth
    > cases, it subs the constant values. It used to be that you would
    > have to define two things, for example, you might have to define both
    > a constant and a variable:
    >
    > pin_as_constant con 2
    > pin_as_variable in2 ' reference as variable
    > if pin_as_variable=0 then skipaction ' reference as constant
    > pulsout 2, 1000
    > skipaction:
    >
    > Now it can be one thing:
    >
    > what_a_pin pin 2
    > if what_a_pin=0 then pulseout what_a_pin,1000
    > ' the compiler sorts it out!
    >
    > -- regards,
    > Tracy Allen
    > electronically monitored ecosystems
    > mailto:tracy@e...
    > http://www.emesystems.com
    >
    >
    >
    >
    > >Hello again!
    > >
    > >I'm attempting to interface an LTC1298CN8 12-bit serial ADC converter to
    a
    > >BS2. For a test, I simply have a 50k pot as a voltage divider from +5 to
    > >ground, with the slider attached to the + input of the ADC. PIN0 is my
    CLK
    > >pin, PIN1 is Dout, PIN2 is Din, and PIN15 is !CS on my stamp. I read the
    > >data into variables called SampleLow and SampleHigh, then debug them to
    the
    > >PC. The code is below. I always get a result of "0:0", so the variables
    do
    > >not seem to be getting chnaged during the SHIFTIN function.
    > >
    > >Any ideas?
    > >
    > >Steve
    > >
    > >
    > >'{$STAMP BS2}
    > >'{$PBASIC 2.5}
    > >
    > >SampleLow VAR byte
    > >SampleHigh VAR Byte
    > >
    > >DEBUG "Startup", Cr
    > >high 15
    > >PAUSE 1000
    > >DEBUG "Entering Main", cr
    > >Main:
    > > LOW 15
    > > SHIFTOUT OUT1, OUT0, LSBFIRST, [noparse][[/noparse]%00011\4]
    > > SHIFTIN IN2, OUT0, LSBFIRST, [noparse][[/noparse]SampleLow\8, SampleHigh\4]
    > > HIGH 15
    > > DEBUG DEC SampleHigh, ":", DEC SampleLow, CR
    > > PAUSE 5
    > >GOTO Main
    > >end
    > >
    >
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