Lec7_InternalMemory_1011 - Lecture 7 Internal Memory CC2202...

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CC2202 1 Lecture 7 Internal Memory
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CC2202 2 Last Week and This Week We learnt Memory Hierarchy Cache Memory operation Mapping Functions We will learn Dynamic and Static Memory Error Correction
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CC2202 3 Semiconductor Memory Operation (5.1) All semiconductor memory cells share certain properties: 1. Two stable states - can be used to represent 2. Capable of being written into (at least once), to set the state. - Store 3. Capable of being read to sense the state. - Data can be
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CC2202 4 Semiconductor Memory Types RAM Dynamic RAM (DRAM) Static RAM (SRAM) ROM PROM EPROM EEPROM Flash Memory
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CC2202 5 Semiconductor Memory Random Access Memory ( ) Misnamed as all semiconductor memory is random access Main Characteristics: Read/Write Volatile + Require a constant power supply Temporary storage Two Forms: Static or dynamic
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CC2202 6 Dynamic RAM (DRAM) Bits stored as charge in capacitors Dynamic refers Charges leak Need refreshing even when powered Need refresh circuits Advantages Simpler construction Smaller per bit Less expensive Disadvantages Slower Applications: Capacitor
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CC2202 7 Dynamic RAM (DRAM) A typical DRAM structure for an individual cell that stores one bit. Transistor acts as a switch that is closed (allowing current to flow) if a voltage is applied to the address line and open (no current flows) if no voltage is on the address line.
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CC2202 8 DRAM Operation Essentially analogue Level of charge determines value Address line active when bit read or written Transistor switch closed (current flows) Write Voltage to bit line High for 1 low for 0 Then signal address line Transfers charge to capacitor Read Address line selected transistor turns on Charge from capacitor fed via bit line to sense amplifier Compares with reference value to determine 0 or 1 Capacitor charge must be restored
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CC2202 9 Static RAM In SRAM, binary values are stored using flip-flop. There are a variety of flip-flops: S-R flip-flop (or S-R Latch) –clocked S-R flip-flop D flip-flop J-K flip-flop
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CC2202 10 S-R Flip-flop The circuit has two inputs, S (Set) and R (Reset) The circuit has two outputs, Q and Q’
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CC2202 11 S-R Flip-flop Q’ is 1 Assume both S and R are 0 and that Q is 0.
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12 S-R Flip-flop At this moment S changes to 1. 0 0 0 1
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Lec7_InternalMemory_1011 - Lecture 7 Internal Memory CC2202...

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