MEMORY AND PROGRAMMABLE LOGIC Flashcards
What is a memory unit
A memory unit is a collection of cells capable of storing a large quantity of binary information, together with associated circuits needed to transfer information into and out of a device
Describe the ROM
Read-only memory(ROM): perform only the read operation.
The ROM is a programmable logic device – Programming (embedding data) is done on hardware. Other such units are the programmable logic array (PLA), the programmable array
logic(PAL), and the field-programmable gate array(FPGA).
A typical programmable logic device may have hundreds to millions of gates interconnected through hundreds to thousands of internal paths.
Describe the storage and communication of data in the RAM
A memory unit stores binary information in groups of bits called words.
1 byte = 8 bits
1 word = 2 bytes
The communication between a memory and its environment is achieved through data input and output lines, address selection lines, and control lines that specify the direction of transfer.
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Describe and illustrate the content of a memory
Each word in memory is assigned an identification
number, called an address, starting from 0 up to 2
k -1, where k is the number of
address lines.
The number of words in a memory with one of the letters
K=210, M=220, or G=230.
64K = 216 2M = 221
4G = 232
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Describe how write and read operations are carried out
Transferring a new word to be stored into memory:
1. Apply the binary address of the desired word to the address lines.
2. Apply the data bits that must be stored in memory to the data input lines.
3. Activate the write input.
Transferring a stored word out of memory:
1. Apply the binary address of the desired word to the address lines.
2. Activate the read input.
Describe the control inputs used in commercial memory for reading and writing
*See page 5
Define access time and cycle time
The access time of memory is the time required
to select a word and read it.
The cycle time of memory is the time required
to complete a write operation.
The access time and cycle time of the memory
must be within a time equal to a fixed number
of CPU clock cycles.
Illustrate the timing waveforms of the write function
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How is destruction of memory words prevented
The memory enable and the read/write signals
must be activated after the signals in the
address lines are stable to avoid destroying data
in other memory words.
What are the different types of memories
In random-access memory, the word locations may be thought of as being separated in space, with each word occupying one particular location.
the access time is always the same regardless of the particular location of the word.
In sequential-access memory, the information stored in some medium is not immediately accessible, but is available only certain
intervals of time. E.g. A magnetic disk or tape.
the time it takes to access a word depends on the position of the word with respect to the reading head position; therefore, the access time is
variable.
Describe static RAM
SRAM consists essentially of internal latches that store the binary information.
The stored information remains valid as long as power is applied to the unit.
SRAM is easier to use and has shorter read and write cycles.
Low density, low capacity, high cost, high speed, high power consumption.
Describe Dynamic RAM
DRAM stores the binary information in the form of electric charges on capacitors.
The capacitors are provided inside the chip by MOS transistors metal–oxide–semiconductor field-effect transistor).
The capacitors tends to discharge with time and must be periodically recharged by refreshing the dynamic memory.
DRAM offers reduced power consumption and larger storage capacity in a single memory chip.
High density, high capacity, low cost, low speed, low power consumption.
DRAMs typically have four times the density of SRAM.
The cost per bit of DRAM storage is three to four times less than SRAM. Another factor is lower power requirement.
Describe volatility in memory
Memory units that lose stored information when power is turned off are said to be volatile.
Both static and dynamic, are of this category since the binary cells need external power to maintain the stored information.
Nonvolatile memory, such as magnetic disk, ROM, retains its stored information after removal of power.
Give some methods of error detection and correction
Parity Method – Error detection method
Hamming Code – Error Correction method
Describe and illustrate the read-only memory
A block diagram of a ROM is shown below. It consists of k address inputs and n data outputs.
The number of words in a ROM is determined from the fact that k address input lines are needed to specify 2k words.
ROM does not have data inputs, because it does not have a write operation.
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