Download Chapter 7 Memory and Programmable Logic

Memory and Programmable
Logic
Chapter 7
Introduction
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RAM: Random Access Memory
ROM: Read Only Memory
Write operation: Storing info into memory
Read operation: Transferring info out of the memory
RAM can perform both Write and Read operations
ROM is a Programmable Logic Device (PLD) that can be
written once and can only be read afterwards
• PLA: Programmable Logic Array
• PAL: Programmable Array Logic
• FPGA: Field Programmable Gate Array
Conventional and array logic diagrams
Random Access Memory
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Memory unit that can be written or read
Memory is composed of “words”
Word is a group of bits
Byte is a group of 8 bits (Denoted B)
Words can have one or more bytes: a word of
32 bits has 4 bytes
• Memory size is normally measured in bytes,
e.g., 1024 bytes = 1KB
Random Access Memory
• When word size is known memory size can be
given in words, e.g., 1 word = 64 bits = 8 bytes.
• 1K requires 10 bits address, i.e., 1024 = 210
• 1M = 220
• 1G = 230
• 4G = 232
• Each word has an id. number called an
address (0 to 2k`-1, where k is the # of address
lines)
Random Access Memory
Random Access Memory
Contents of a 1K x 16
memory
Write and read operations
• Read and write take the same time, regardless
of location; contrast with magnetic tape; read
may take different time from write operation
• Write: transfer-in operation
• Read: transfer-out operation
Write and read operations
• Steps to store a new word into memory
1. Apply binary address of desired word to address
lines (k)
2. Apply data bits that must be stored in memory
to data input lines (nin)
3. Activate the write input
• Memory unit will take bits from input data
lines and store them in word specified by
address lines
Write and read operations
• Steps to read a word out of memory
1. Apply desired binary address of desired word to
address lines
2. Activate the read input
• Memory unit will take bits from word
specified by address lines and apply them to
output data lines
Write and read operations
Control inputs in typical commercial memory chips
Timing waveforms
Cycle time: time required to finish a write operation
Timing waveforms
access time: time required to finish a read operation
Timing waveforms
Cycle Time
(i.e. Write Time)
T = 1/fCLK
CPUCLK
ADDRESS
ADDRESS VALID
MEMORY SELECT
DATA VALID FOR WRITE
DATA VALID
FOR READ
Types of memories
• Static RAM or SRAM: consists of internal
latches that store binary information
• Dynamic RAM or DRAM: stores information in
form of electric charge on capacitors provided
by MOS transistors inside the chip, thus
requires refresh every few ms
• Volatile memory lose stored information when
powered off. Magnetic memory is nonvolatile.
ROM is another type of nonvolatile memory
Types of memories
• DRAM refreshing requires cycling through
words every few ms to restore decaying
charge
• DRAM offers reduced power consumption and
larger storage capacity in a single chip
• SRAM is easier to use
Bonus Assignment: find out what Flash
Memories are and how they are used
Memory Decoding
Memory Decoding
Coincident decoding
LSB
MSB
• Decoder with k
inputs and 2k
outputs requires
2k AND gates
• A 1K memory
requires a
10x1024 decoder
• Use instead a 2-D
selection patter
and 1K requires
two 5x32
decoders!
• Word is selected
by coincidence of
one X and one Y
line
Address multiplexing
• SRAMs contain 6 transistors per cell
• DRAMs contain one MOS transistor and one
capacitor per cell
• DRAMs achieve higher storage capacity per unit
area – four times that of a SRAM - and lower
power consumption
• DRAM typical word size = 1 bit
• DRAM is preferred for large memories for PCs
• DRAM available from 64K to 256M bits
• To reduce number of pins, thus chip size, use
address multiplexing
Address multiplexing
• Capacity = 256x256 =
28x28 =64K
• RAS = Row Address
Strobe
• CAS = Column Address
Strobe
Error Detection and Correction
• Dynamic physical interaction of electrical
signals may cause occasional errors
• Memories can use two types of codes:
– Error detection codes, parity (chapter 3)
– Error correction codes
Error Detection and Correction
• Hamming code
– Error correction code
– Uses several parity bits per word
– Can detect and correct 1-bit errors
Hamming code
Bit
position
1
2
3
4
5
6
7
8
9
10
11
12
P1
P2
1
P4
1
0
0
P8
0
1
0
0
Parity generation equations
𝑃1 = 𝐸𝑋𝑂𝑅(3,5,7,9,11)
𝑃2 = 𝐸𝑋𝑂𝑅(3,6,7,10,11)
𝑃4 = 𝐸𝑋𝑂𝑅(5,6,7,12)
𝑃8 = 𝐸𝑋𝑂𝑅(9,10,11,12)
Check bit equations (Syndrome)
𝐶1 = 𝐸𝑋𝑂𝑅(1,3,5,7,9,11)
𝐶2 = 𝐸𝑋𝑂𝑅(2,3,6,7,10,11)
𝐶4 = 𝐸𝑋𝑂𝑅(4,5,6,7,12)
𝐶8 = 𝐸𝑋𝑂𝑅(8,9,10,11,12)
Hamming code
Bit
1
2
3
4
5
6
7
8
9
10
11
12
No error
0
0
1
1
1
0
0
1
0
1
0
0
Bit 1 error
1
0
1
1
1
0
0
1
0
1
0
0
Bit 5 error
0
0
1
1
0
0
0
1
0
1
0
0
Hamming code
Syndrome
Position
of error
C8
C4
C2
C1
No error
0
0
0
0
1
0
0
0
1
2
0
0
1
0
3
0
0
1
1
4
0
1
0
0
5
0
1
0
1
6
0
1
1
0
7
0
1
1
1
8
1
0
0
0
9
1
0
0
1
10
1
0
1
0
11
1
0
1
1
12
1
0
0
0
Single-error correction, double-error
detection
Read-Only Memory
Read-Only Memory
Read-Only Memory
Read-Only Memory
ROM programming according to table 7.3
Combinational circuit implementation
• ROM uses a decoder for address and decoder
gives minterms
• Outputs use OR gates thus ROM can be seen
as:
– A storage device
– Combinational circuit implementing Boolean
functions
Combinational circuit implementation
Example
Example 7.1: ROM-based circuit that accepts a three-bit number and produces a
binary number equal to the square of the input number.
Combinational circuit implementation
Example
Types of ROM
• Mask programming: done by semicondutor
company during last fabrication process of unit
• PROM (Programmable ROM): Programming by
blowing fuses by applying a high voltage; blown
fuse outputs a 0
• EPROM (Erasable PROM): Erase using special
ultraviolet light
• EEPROM or E2PROM (Electrically Erasable PROM)
Combinational PLDs
Programmable Logic Array
Exercise: Obtain the equations for this PLA.
What role do the EXOR gates play?
Programmable Logic Array
Example 7.2
Implement the following two Boolean functions with a PLA:
𝐹1 𝐴, 𝐵, 𝐶 =
0,1,2,4
𝐹2 𝐴, 𝐵, 𝐶 =
0,5,6,7
What do we have to do?
Obtain minimum number of terms as sum of products
𝐹1 𝐴, 𝐵, 𝐶 = 𝐴′ 𝐵′ + 𝐴′𝐶 ′ + 𝐵′𝐶′
𝐹2 𝐴, 𝐵, 𝐶 = 𝐴𝐵 + 𝐴𝐶 + 𝐴′𝐵′𝐶′
Programmable Array Logic
Example of PAL Programming
Example of PAL Programming
Sequential Programmable Devices
Sequential Programmable Devices
• SPLD: Sequential Programmable Logic Device
• CPLD: Complex Programmable Logic Device
Sequential Programmable Devices
Basic macrocell logic
Sequential Programmable Devices
CPLD
Sequential Programmable Devices
Architecture of
Xilinx Spartan
FPGA (Field
Programmable
Gate Array
Sequential Programmable Devices
Configurable Logic
Block (CLB)
Sequential Programmable Devices
RAM cell controlling a PIP transmission
gate
Exercises
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7.1
7.2
7.3
7.4
7.6
7.7
7.8
7.9
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7.10
7.14
7.15
7.18
7.19
7.20
7.23
7.24
P7.26
Sequential Programmable Devices
IOB of XC4000
Series