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/* This module converts a user specified coordinates into a memory address.
* The output of the module depends on the resolution set by the user.
*/
module vga_address_translator(x, y, mem_address);
parameter RESOLUTION = "320x240";
/* Set this parameter to "160x120" or "320x240". It will cause the VGA adapter to draw each dot on
* the screen by using a block of 4x4 pixels ("160x120" resolution) or 2x2 pixels ("320x240" resolution).
* It effectively reduces the screen resolution to an integer fraction of 640x480. It was necessary
* to reduce the resolution for the Video Memory to fit within the on-chip memory limits.
*/
input [((RESOLUTION == "320x240") ? (8) : (7)):0] x;
input [((RESOLUTION == "320x240") ? (7) : (6)):0] y;
output reg [((RESOLUTION == "320x240") ? (16) : (14)):0] mem_address;
/* The basic formula is address = y*WIDTH + x;
* For 320x240 resolution we can write 320 as (256 + 64). Memory address becomes
* (y*256) + (y*64) + x;
* This simplifies multiplication a simple shift and add operation.
* A leading 0 bit is added to each operand to ensure that they are treated as unsigned
* inputs. By default the use a '+' operator will generate a signed adder.
* Similarly, for 160x120 resolution we write 160 as 128+32.
*/
wire [16:0] res_320x240 = ({1'b0, y, 8'd0} + {1'b0, y, 6'd0} + {1'b0, x});
wire [15:0] res_160x120 = ({1'b0, y, 7'd0} + {1'b0, y, 5'd0} + {1'b0, x});
always @(*)
begin
if (RESOLUTION == "320x240")
mem_address = res_320x240;
else
mem_address = res_160x120[14:0];
end
endmodule
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