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Favre04 Guest
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output pins |
Posted: Fri Dec 31, 2004 9:10 am |
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I have been trying to write a keypad program that lights up an array of twelve led's. In order to save IO lines, I have decoded the locations. However, I would like to use only one write function. This would require being able to pass which pin to output to through a function. My decoding scheme decides which pin is applicable, then I output. When compiling I get this error. I know data_line should be a constant, but is there anyway to get around this.
Quote: | *** Error 27 "C:\Documents and Settings\sshill.PELHAM\Desktop\MY Code\Keys\keydriver.c" Line 235(54,55): Expression must evaluate to a constant |
Code: | #define row1data PIN_D1
#define row2data PIN_D2
int data_line;
int button_id;
if (button_id < 3)
{
data_line = row1data;
}
if (button_id > 6)
{
data_line = row2data;
}
output_bit(data_line, shift_left(&commandbyte[j],1,0)); |
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rnielsen
Joined: 23 Sep 2003 Posts: 852 Location: Utah
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Posted: Fri Dec 31, 2004 9:27 am |
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The function output_bit() requires a constant, like the number 45 or PIN_D1(which has been previously defined in the devices file for the part). You are trying to use a variable, data_line, as part of the function. Read the help file on this function a bit more.
Ronald |
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Ttelmah Guest
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Posted: Fri Dec 31, 2004 10:09 am |
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Why not just go one stage further in what you have already done?.
Code: |
#define row1data PIN_D1
#define row2data PIN_D2
int bit_val;
int button_id;
bit_val=shift_left(&commandbyte[j],1,0);
if (button_id < 3)
{
output_bit(row1data,bit_val);
}
if (button_id > 6)
{
output_bit(row2data,bit_val);
}
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If you need to access multiple bits in a single byte, you can just use a bit mask, and the byte IO functions. The 'bit' IO functions, all require constant values, not variables.
Best Wishes |
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FAvre04 Guest
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thanks |
Posted: Fri Dec 31, 2004 4:27 pm |
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Thanks for your suggestions. I was hoping there was a way to around the constant problem. But i can just code it out with switch statements. |
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