ECE 301 – Digital Electronics Memory (Lecture #22)
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Transcript of ECE 301 – Digital Electronics Memory (Lecture #22)
ECE 301 – Digital Electronics
Memory
(Lecture #22)
Random Access Memory
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Random Access Memory
Static Random Access Memory (SRAM)
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Random Access Memory
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Address Decoding
Random Access Memory
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RAM: Address Decoding
k-bit address Decoder requires 2k AND gates
Each AND gate has k inputs For large k this becomes prohibitive.
Use 2-dimensional decoding Two decoders Each decoder requires 2(k/2) AND gates
Each AND gate has k/2 inputs Far less combinational logic
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RAM: Address Decoding
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RAM: Address Decoding
The size of a chip package is often dictated by the number of input and output signals.
For large memories, the number of address lines often becomes prohibitive.
Use address multiplexing The same address lines are used both for
the row address and the column address Use time multiplexing to first latch the row
address and then latch the column address
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RAM: Address Decoding
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Random Access Memory
Building a Bigger Memory System
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RAM Systems
Often RAM chips are smaller than the required memory size.
What if you need a wider memory? Larger word size
What if you need a deeper memory? Greater number of memory locations
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RAM Systems
Exercise:
Design a 32K x 32 memory usingRAM chips that are 32K x 8.
How many address bits are required?How many data bits are required?
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Exercise: 32K x 32 RAM
Addr Addr Addr Addr15
A14
- A0
D31
- D24
8 8 8 8
D23
- D16
D15
- D8
D7 - D
0
Data Data Data Data
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RAM Systems
Exercise:
Design a 128K x 8 memory usingRAM chips that are 32K x 8.
How many address bits are required?How many address bits are connected to the RAM chips?
What are the remaining address bits connected to?
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Example: 128K x 8 RAM
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Read Only Memory
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Read Only Memory ROM store “permanent” binary information
One-time programmable memory Multiple-time programmable memory
Address and Data k address bits n data bits
2k x n ROM includes k-to-2k decoder n 2k-input OR gates
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Read Only Memory
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Read Only Memory
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Read Only Memory
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Read Only Memory
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Read Only Memory
EEPROM (E2PROM) Electrically Erasable Programmable ROM
Flash ROM Similar to E2PROM Has additional circuitry to selectively erase
and program the memory in-circuit Does not require a special programmer
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Programmable Logic Devices
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Programmable Logic Devices
Programmable Logic Arrays (PLA) Programmable Array Logic (PAL) Simple Programmable Logic Device (SPLD) Complex Programmable Logic Device (CPLD) Field Programmable Gate Array (FPGA)
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“That's All Folks!”
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Acknowledgments
The slides used in this lecture were taken, with permission, from those provided by Pearson Prentice Hall for
Digital Design (4th Edition).
They are the property of and are copyrighted by Pearson Education.