In VHDL language what the underscore exactly mean in natural no.

[rourabpaul]

I have a Syntax in VHDL from net

generic(

FREQ : natural := 100_000
);

I cnt understand the natural value of FREQ,what the underscore exactly meaning in that case

 

[alexan_e]

The underscore is just used for readability, in your code it is probably used as a thousand separator, the number is 100000 , you could even write it as 10_00_00 and it would still be the same number.

Alex

 

[rourabpaul]

Thank you Alex,
one another syntax meaning i want to know

parity <= sc_r(scancode'high+1);
here scancode is a 8 bit ,sc_r is 10 bit and parity is one bit std logic type

 

[alexan_e]

when you have a scancode (7 downto 0) then scancode'high=7

Alex

---------- Post added at 13:24 ---------- Previous post was at 13:19 ----------

I think will help you with some examples
VHDL Resolution and Signatures

Alex

 

[rourabpaul]

u mean
parity<=sc_r( 8 )

 

[alexan_e]

7+1=8
yes

Alex

 

[rourabpaul]

I have another syntax problem
the code is
" scancode <= sc_r(scancode'range);"
here scan code is 8 bit,and sc_r is 10 bit
thank you in advance

 

[alexan_e]

In the link i have provided above there are examples for this also

[B]A : std_logic_vector(31 downto 0)[/B] := x"FEDCBA98"; -- 'downto'
[B]B : std_logic_vector( 4 to    27) [/B]:= x"654321";   -- 'to'
C       a literal constant                  x"321"

Name  bitstring (attributes on following lines)

 A    11111110110111001011101010011000
      A'left=31     A'right=0      A'low=0      A'high=31
      A(A'left)=1   A(A'right)=0   A(A'low)=0   A(A'high)=1
      [B]A'range=(31 downto 0)[/B]        A'reverse_range=(0 to 31) 
      A'length=32                  A'ascending=false

 B    011001010100001100100001                  B'ascending=true
      B'left=4      B'right=27     B'low=4      B'high=27
      B(B'left)=0   B(B'right)=1   B(B'low)=0   B(B'high)=1
      [B]B'range=(4 to 27) [/B]           B'reverse_range=(27 downto 4) 
      B'length=24                  B'ascending=true

 C    001100100001
      C'left=0      C'right=11     C'low=0      C'high=11
      C(C'left)=0   C(C'right)=1   C(C'low)=0   C(C'high)=1
      [B]C'range=(0 to 11) [/B]           C'reverse_range=(11 downto 0) 
      C'length=12                  C'ascending=true

Alex