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Memory and Repetitive Arithmetic Machines

Prof. Sirer CS 316 Cornell University. Memory and Repetitive Arithmetic Machines. Memory. Various technologies S-RAM, D-RAM, NV-RAM Static-RAM So called because once stored, data values are stable as long as electricity is supplied Based on regular flip-flops with gates Dynamic-RAM

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Memory and Repetitive Arithmetic Machines

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  1. Prof. Sirer CS 316 Cornell University Memory and Repetitive Arithmetic Machines

  2. Memory • Various technologies • S-RAM, D-RAM, NV-RAM • Static-RAM • So called because once stored, data values are stable as long as electricity is supplied • Based on regular flip-flops with gates • Dynamic-RAM • Data values require constant refresh • Internal circuitry keeps capacitor charges • Non-Volatile RAM • Data remains valid even through power outages • More expensive • Limited lifetime; after 100000 to 1M writes, NV-RAM degrades

  3. S-RAM Data • A decoder selects which line of memory to access • A R/W selector determines the type of access • That line is then coupled to the data lines • How do you build large memories? Address Decoder

  4. Tristate Buffers • A device that couples a logic line to a wire

  5. Big Memories data enable • Memory banks in parallel, with tri-state buffer and decoder to select which bank to couple • The enable bit controls connection of data bits and clocking of internal flip-flops 2 12 addr

  6. Summary • We now have enough building blocks to build machines that can perform non-trivial computational tasks

  7. A Calculator • User enters the numbers to be added or subtracted using toggle switches • User selects ADD or SUBTRACT • Muxes feed A and B,or A and –B, to the 8-bit adder • The 8-bit decoder for the hex display is straightforward (but not shown in detail) 8 … reg 8 led-dec adder 8 8 … mux reg 8 0 1 mux add/sub select doit

  8. A Vote Counter led-dec 8 reg • Data values flow from set of parallel registers (a register file) • to the addition unit • back into the register file 8 s1 .. mux 8 reg 1 0 clk s4 s4 s3 reg enc deco s2 s1

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