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Altera_Forum's avatar
Altera_Forum
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19 years ago

Reading from an 8 Bit Component

Hi,

I connected the Nios to an 8 bit custom component. When I read from a register which contains a 1 as the most significant bit, i.e. all values from 0x80 to 0xFF, the remaining 24 bits get filled up with 1's.

For example reading the value 0x70 residing in one of the component's registers gives the value 0x00000070 to the variable I'm saving it to. But reading 0x80 gives the value 0xFFFFFF80.

So I guess the values are treated as signed values, which would explain why it fills the remaining bits with 1's.

But how can I prevent that?

Thanks in advance

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    19 years ago

    Hi stic,

    > For example reading the value 0x70 residing in one of the component's registers gives the

    > value 0x00000070 to the variable I'm saving it to. But reading 0x80 gives the value 0xFFFFFF80.

    If you're reading an 8-bit unsigned value, it's a good idea to store it as an 8-bit unsigned

    variable ;-)

    unsigned char foo = <<whatever>>

    Regards,

    --Scott
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    19 years ago

    --- Quote Start ---

    originally posted by smcnutt@Jan 19 2007, 09:51 AM

    if you&#39;re reading an 8-bit unsigned value, it&#39;s a good idea to store it as an 8-bit unsigned

    variable ;-)

    <div align='right'><{post_snapback}> (index.php?act=findpost&pid=20715)

    --- quote end ---

    --- Quote End ---

    Yes, indeed it is a very good idea to use unsigned char...

    I didn&#39;t think of this before.

    Thanks a lot, Scott