More Digital circuits
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Transcript of More Digital circuits
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More Digital circuits
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Ripple Counter
• The most common counter• The problem is that,
because more than one output is changing at once, the signal is glichy
• To avoid this problem, use Gray or Johnson code
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Johnson Counter
• The Johnson counter is type of shift counter
• Put an inverted MSB back to LSB
• Glitch output free
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Johnson Counter with error recovery
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Linear Feedback Shift Registers
• A small number of taps are recycled
• An LFSR can operate at high speed compared to a binary counter because the feedback logic is very simple
• Reduce clock noise
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Many-to-One LFSR
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Many-to-One LFSR
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Maximal length LFSR
• With maximal length logic (taps selected to give
the maximal count),a small number
of register can create sequence up to 2n-1
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Divide by N LFSR Counter
• An example of the use of a LFSR
• A terminal count is provided as an input to be compared to
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Divide by N LFSR Counter
• Test fixture
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4-Bit LFSR One-to-Many Code
• One-to-Many variant splits the XOR into 2-input gates and distributes them throughout the register array
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Cyclic Redundancy Checksums
• Error detection• The data packet is
looked at as a huge binary number
• A polynomial divide this number in GF
• Reminder is checksum
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Cyclic Redundancy Checksums
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ROM
• ROM stands for Read-Only Memory• This memory is initialized when
the FPGA is configured and cannot be changed after configuration
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ROM Version of LFSR
• We can implement four-bit LFSR counter with a ROM
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RAM
• RAM stands for Random Access Memory
• A RAM is an array of cells, addressable in groups N element wide and M elements deep
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RAM
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RAM
• Unless the FPGA support embedded RAM blocks, it will consume a huge amount of logic
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FPGA with embedded RAM
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256x8 RAM Implemented in the 4000XL Device Family
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Dual port RAM
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• Jovan Popovic [email protected]• Milos Milovanovic [email protected]• Veljko Milutinovic [email protected]• Nobelovac?