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ecenus 09-22-2008 02:37 PM

Data type used in VHDL

I am newbie to VHDL design. I came across a question of using VHDL.

I'd like to output a 17 bit data through one port (one pin in an Altera chip) to my DSP on the the same circuit board. Each bit, either 0 or 1, stands for an error detected in my circuit. Say, if the second bit turns to 1, I will know something is wrong with my temperature sensor....

But, when I set the port as STD_LOGIC_VECTOR (0 To 16), I got the error message that I can not send such data through one pin but 17 pins....

Now, I want to know if I want to send my 17-bit data through one port. What data type should I use?

Your help is highly appreciated!


Steff 09-22-2008 03:01 PM


if a one stays for an error, you can do this:

PHP Code:

library ieee;

signal s_error_vec  std_logic_vector(0 to 16);
signal s_error_flag std_logic;


<= or_reduce(s_error_vec); 

Did you means this?

Bye, Steff

ecenus 09-22-2008 03:11 PM

Hi, Steff,

Thank you for your reply.

Maybe I did not indicate it clearly in my last post. I actually set the code like this:

data_out: OUT STD_LOGIC_VECTOR (0 TO 16));

CASE fault_count IS
WHEN 0 => data_out(0) <= flt1;
WHEN 1 => data_out(1) <= flt2;
WHEN 2 => data_out(2) <= flt3;
WHEN 3 => data_out(3) <= flt4;
WHEN 4 => data_out(4) <= flt5;
WHEN 5 => data_out(5) <= flt6;
WHEN 6 => data_out(6) <= flt7;
WHEN 7 => data_out(7) <= flt8;
WHEN 8 => data_out(8) <= flt9;
WHEN 9 => data_out(9) <= flt10;
WHEN 10 => data_out(10) <= flt11;
WHEN 11 => data_out(11) <= flt12;
WHEN 12 => data_out(12) <= flt13;
WHEN 13 => data_out(13) <= flt14;
WHEN 14 => data_out(14) <= flt15;
WHEN 15 => data_out(15) <= flt16;
WHEN 16 => data_out(16) <= flt17;

But, I set "data_out" at PIN_K20, which is just one pin. but I was told the system requires 17 pins. I think I made a mistake here. Do you know what data type I should set "data_out" and set each bit standing for one error bit required in my design?

Thanks, again!


Steff 09-23-2008 02:07 PM

Hi ecenus,

std_logic_vector is the right type for your design.

If you want to transmit this vector you have two different approaches:

1. sequentiell design:
You have one pin and you have to send your data bit by bit. 5 clocks would be enough. (1 bit of the error message/clock cycle)

2. parallel design:
You have more than one pin. Then you can transmit your data in parallel. 5 pins would be enough. (1 error message/ clock cycle)

If its enough only to see whether an error was occured then you can take the method I told you already at the last post.

At present I have no further ideas.


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