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Altera_Forum's avatar
Altera_Forum
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15 years ago

question regarding VGA tutor in "Rapid Prototyping of Digital Systems"

Hi,

I'm doing the VGA tutorial from the "Rapid Prototyping of Digital Systems-SOPC" book.

In page 202 of the book, in the CHAR ROM chapter, there's a line:

rom_mux_output <= rom_data (CONV_INTEGER( not font_col( 2 downto 0 ))) );

I would be very happy if someone could explain this line to me...

The rom_mux should choose 1 bit from 8 bit word it has in the CHAR ROM memory. the font_col says which line it chooses in order to show the letter 'A' (for example) on the screen. (the letter A is made of eight 8-bit words, each word is 8 pixels which forms the letter A)

Why conv_integer is needed?

why is there a NOT function before the font_col?

Any help would be very appreciated...

Thank you!

Roy

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    ok, found the answer from some code on the net:-- Mux to pick off correct rom data bit from 8-bit word-- This is needed because while the column count goes from left to right on screen,-- the same pixels are indexed from right to left in rom_data. rom_mux_output

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

    -- Mux to pick off correct rom data bit from 8-bit word-- This is needed because while the column count goes from left to right on screen,-- the same pixels are indexed from right to left in rom_data. rom_mux_output