More Digital circuits
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Transcript of More Digital circuits
More Digital circuits
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
Johnson Counter
• The Johnson counter is type of shift counter
• Put an inverted MSB back to LSB
• Glitch output free
Johnson Counter with error recovery
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
Many-to-One LFSR
Many-to-One LFSR
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
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
Divide by N LFSR Counter
• Test fixture
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
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
Cyclic Redundancy Checksums
ROM
• ROM stands for Read-Only Memory• This memory is initialized when
the FPGA is configured and cannot be changed after configuration
ROM Version of LFSR
• We can implement four-bit LFSR counter with a ROM
RAM
• RAM stands for Random Access Memory
• A RAM is an array of cells, addressable in groups N element wide and M elements deep
RAM
RAM
• Unless the FPGA support embedded RAM blocks, it will consume a huge amount of logic
FPGA with embedded RAM
256x8 RAM Implemented in the 4000XL Device Family
Dual port RAM
• Jovan Popovic [email protected]• Milos Milovanovic [email protected]• Veljko Milutinovic [email protected]• Nobelovac?