Forum: FPGA, VHDL & Verilog VGA problem in Verilog

Author: Xavier Pacheco (Company: PUCMM) (xavi07p)
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I have the the Pong Game code in Verilog with FPGA Xilinx Spartan 
Everything works well, but I notice some flickering in the monitor, 
something like vibrations. What do you think? What is the problem? Maybe 
noisy clock?
Thank you.

Author: Sigi (Guest)
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In general, it's impossible to answer without your source code.
But the Basys2 is well known in e.g. classic fpga computing for
it's bad clock, more exactly, it's a jitty oscillator. This is
often the source of pixel jittering.
AFAIK the board has an 8-pin socket for an extra clock source.

Author: Verilogi (Guest)
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if there is a pll used, the clock should be fine. small clock problems 
usually lead only to bad pixels. if there is flickering, a bad 
constellation between hsynch and vsynch is given usually

most probably also a unsynched updating process of the screen will be 
the problem to solve


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