Thread: Please Help! Urgent!

  1. #1
    Registered User
    Join Date
    Feb 2003

    Wink Please Help! Urgent!

    I need to write a programe executable in DOS to control a hardware, a 12-bit analog-to-digital converter card using C++. I've the manual about this card and the procedures to develop the programe is given. However, i have many uncertainties about the procedures. Would any one help to solve them.

    Here I show briefy the manual as below(deails of manual refer to attachment
    The I/O port address are &h278-27F or &H2F8-2FF selectable.
    &H278 / 2F8 : Output A/D channel number. (low nibble).
    279 / 2F9 : Input A/D low byte data. (8 bits).
    27A / 2FA : Input A/D high byte data.
    27B / 2FB : Clear A/D register.
    27C / 2FC : A/D conversion loop. (low)
    27D / 2FD : A/D conversion loop (high)
    27E / 2FE : Output D/A low byte data. (8 bits)
    27F / 2FF : Output D/A high byte data. (low nibble).

    Analog to digital (A/D) procedure:
    (1) Output channel number to port

    OUT port channel

    (2) Clear register

    OUT (port + 3), 0

    (3) Start convert
    FOR I=1 to 5
    A = INP (port + 4)
    NEXT I=1 TO 9
    A = INP (port + 5)
    NEXT I

    (4) Read high byte (low nibble)
    C = INP (port + 2)
    HB = (C/16 íV INT (C/16)) * 16

    (5) READ LOW BYTE (8 BITS)
    LB = INP (port + 1)

    (6) Data:
    A/D = HB * 256 + LB

    My questions are:
    1. In procedure (3), it seems that there should be two for-loop, one inside another, is there a typing error in the guideline. And if it is so, why should it take a total 45 times 'INP'. What's the purpose of that?

    2. In procedure(4), to my understanding, INP(port +2) return the high byte from a 12-bit data. So, why shouldn't I directly multiply it by 256 to shift it by 8 bits higher like that is done in
    procedure(6)? what's the use of that?

    3. I've writen my own programe and compiled it using Turbo C++ 3, but some unexpected result usually obtained. I use "inp()" to get the HOB and LOB, but the HOB is always equal to 255 while the LOB results in range from 0- 194. Why is it so? Pls give comments on my programe (

    Any help is apprepicate! Thanks

  2. #2
    Registered User Codeplug's Avatar
    Join Date
    Mar 2003
    That is the worst documentation I've ever seen!!! It is incorrect and imcomplete. Notice the "GOSUB 550" in the test program - there is no line 550!!
    You could never get A/D to work with that kind of documentation.

    From you questions:
    1) Yep, that's a "typing error". This is how they sample and convert.

    2) "(C/16 - INT (C/16)) * 16" is just taking the lower nibble (4 bits) of C. This is because it's a 12bit A/D (4 bits in the hight byte and 8 bits in the low byte)

    3) Well, I found the German version of the documentation!!! And it has Pascal and C source! I've attached the documentation I found. It looks like this documentation had several "typing error's" as well, but I combined all the info together to come up with something that hopefully is correct.
    #include <iostream.h>
    #include <dos.h>
    //convenient types
    typedef unsigned short WORD;
    typedef unsigned char  BYTE;
    //Port# card if configured for
    const WORD PORT = 0x278;
    //Millisecond delay to use during conversion...
    //this was used in the Pascal version of the code, I would reduce this # until 
    //it stops working correctly
    const WORD MS_DELAY = 100;
    //Function to perform A/D conversion on given channel (0-15)
    WORD ad(BYTE channel);
    int main()
        for (BYTE n = 0; n < 16; n++)
            cout << "A/D on channel " << n << " is " << ad(n) << endl;
        return 0;
    WORD ad(BYTE channel)
        //check parameter
        if (channel > 15)
            channel = 15;
        //select channel
        //clear register
        //perform sampling/conversion
        int i;
        for (i = 0; i < 5; i++)
        for (i = 0; i < 9; i++)
        //return lower 12bits of result
        return inport(PORT+1) & 0x0FFF;

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