Chat 6 Summary.docx

CHAPTER 6: Summary

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Latch or Flip-Flops – a logic circuit that can remember.

Types: 1. 2. 3. 4.

SR D JK T

• RAM - allows data items to be read or written in almost the same amount of time respective to the physical location of data inside the memory. • RAM should be known as RWM (Read–Write Memory) and PROM as WORMM (Write Once Read Many Memory). • EPROM - a type of memory chip that retains its data when power supply is off. • PROM - digital memory where data in them is permanent and cannot be changed. • STATIC MEMORY - a lot of flip-flops. • SRAM - is constructed from the thousand of flip-flops - fastest but most expensive ROM used in computers. • DRAM - employs totally different approach in storing bits -storing capacity is 256Mbit-1Gbit. -access speed ranges from 50ns-5ns.

TYPES OF MEMORY CHIPS: 1. 2. 3. 4. 5. 6.

RAM ROM PROM EPROM EEPROM FLASH

•DRAM Two Dimensional Array of Capacitor Memory Cell: 1. CAS – column access which are made up of bit lines. 2. RAS – row access which are made up of work line • CYCLE TIME – a delay in which every access, the column, bit lines need time to recharge before the next cycle take place • EDO or Extended Data Output – is a technique that carries out in a burst four access cycle on each read-write request. • Extra Decode Logic – needed to select the memory chip during a read or write cycle. • Memory Maps – describes the location in address space of the chips that are to be installed. • Memory Mapped IO – method that includes IO ports within the same addressing space as memory chips. • IO Mapping – ports are seen in a different address space in memory. • S-R Latch – simplest practicable 1 bit memory cell that can be constructed from two crosscoupled NOR gates. • DRAM – uses small integrated capacitors to store electrical charge to represent a binary 1. • Memory Length – is determined by the address width. • A variety of technologies are used to manufacture memory packages with different characteristics: DRAM, SRAM, EPROM, flash RAM and EEPROM. The main memory in current digital computers is made up of SDRAM (Synchronous DRAM) chips. • IO ports may be memory mapped or installed in a separate IO address space. Here they will require special instructions for access. • Simple input and output ports can appear to a program as single bytes of memory within the address space. • Memory Address Decoding Circuit – this uses some of the remaining upper address lines, which are fed into a separate decoder. The decoder lines are then connected to the chip select (C/S) pins on the memory packs to complete the addressing. Any unused upper address lines can be left for future expansion. • Memory Cards – are designed with refresh circuitry included, increasing the hardware complexity and cost • Method of bursting allows the SDRAM to provide a 5–1–1–1 access performance, and even 3–1–1–1, in some devices