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Advance Computer Architecture

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Advanced Computer Architecture-CS501
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Advanced Computer Architecture
Lecture No. 37
Reading Material
Vincent P. Heuring & Harry F. Jordan
Chapter 7
Computer Systems Design and Architecture
7.1, 7.2
Summary
CPU to Memory Interface
Static RAM cell Organization and Operation
One & two Dimensional Memory Cells
Matrix and Tree Decoders
Dynamic RAM
CPU to Memory Interface
The memory address register (MAR) is m-bits wide and contains memory address
generated by the CPU directly connected to the m-bit wide address bus. The memory
buffer register (MBR) is w-bit wide and contains a data word, directly connected to the
data bus which is b-bit wide. The register file is a collection of 32, 32-bit wide registers
used for data transfer between memory and the CPU. Memory address ranges from 0 to
2m-1.There also exist three control signals:
, REQUEST, and COMPLETE. When
signal is high, this would correspond to a read operation equivalent to having an
input data to the CPU and output from the memory. If this signal is low then it would be a
write operation and data would come from the CPU as an output and it would be written
into a portion in the memory. In this case, the REQUEST signal coming from the CPU
telling the memory that some interaction is required between the CPU and memory. As a
result of this request (either read/write), along with the signal on the control and the
address on the address bus, we might have the corresponding data on the data bus for a
read operation and after the operation is complete, the memory would issue a control
signal which corresponds in this case to COMPLETE.
Figure 7.1 of the text book.
Static RAM Cell Organization and Operation
A Typical Memory Cell
A memory cell provides four functions: Select, DataIn, DataOut, and Read/Write. DataIn
means input and DataOut means output. The select signal would be enabled to get an
operation of Read/Write from this cell.
Figure 7.3 of the text book.
18 Memory Cell Array (1D)
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Advanced Computer Architecture-CS501
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In this arrangement, each block is connected through a bi-directional data bus
implemented with 2 tri-state buffers.
and Select signals are common to all these
cells. This 1-dimentional memory array could not be very efficient, if we need to have a
very large memory.
48 Memory Cell Array (2D)
In this arrangement, 48 memory cell array is arranged in 2-dimensions. At the input, we
have a 24 decoder. Two address bits at the input A0 and A1 would be decoded into 4
signal specifies
select lines. The decoder selects one of four rows of cells and then
whether the row will be read or written.
A 64k1 Static RAM Chip
The cell array is indicated as 256 256. So, there would be 256 rows and 256 columns.
A 64k 1 cell array requires 16 address lines, a read/write line,
, a chip select line,
CS, and only a single data line. The lower order 8-address lines select one of the 256
rows using an 8-to-256 line row decoder. Thus the selected row contains 256 bits. The
higher order 8-address lines select one of those 256 bits. The 256 bits in the row selected
flow through a 256-to-1 line multiplexer on a read. On a memory write, the incoming bit
flows through a 1-to-256 line demultiplexer that selects the correct column of the 256
possible columns.
A 16k4 Static RAM Chip
In this case, memory is arranged in the form of four 64256 memory cells. Four bits can
be read and written at a time. For this, we use one 8-256 row decoder, four 64-1 muxes
and four 1-64 de muxes. The lower address lines (A0-A7) are decoded into 28 lines, 26
lines from these 28 are used to select row from one of the four 64256 cell array and the
remaining 22 lines are used to select one of the 64256 cell array. Now the upper address
lines (A8-A13) are input into the 4 muxes and their output is used to select the required
column from the four 64256 cell arrays. Control lines read/write,
, chip select, CS,
are just similar to previous arrangement.
Matrix and Tree Decoders
A typical one level decoder has n inputs and 2n output, using one level of gates, each with
a fan-in of n. Two level decoders are limited in size because of high gate fan-in. In order
to reduce the gate fan-in to a value of 8 or 6, tree and matrix decoders are utilized.
Six Transistor SRAM Cell
In this arrangement, the cross connection is through inverters to make the latch, the basic
storage cell. This implementation uses six transistor cells. One transistor is used to
implement each of the two inverters, two transistors are used to control access to the
inverters for reading and writing, and two are used as active loads.
SRAM Read Operation
First of all, the CPU provides the address on the external address bus. The read/write
signal becomes active high. After time "tAA", the data becomes available on the data bus.
The chip retains this data on the data lines until the control signals are de asserted.
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SRAM Write Operation
In the case of write cycle, the major difference is that along with the address the CPU has
also provided the data on the data bus. The chip select, CS, is immediately provided and
write signal is made low. The
line must be held valid for a minimum time interval
tw , the write time, until data, address, and control information have been propagated to
the cell and strobe into it. During this period the data lines must be driven with the data to
be written.
Dynamic RAM
As an alternate to the SRAM cell, the data can be stored in the form of a charge on a
capacitor (a charging/discharging transistor that can become a valid memory element),
and this type of memory is called dynamic memory. The capacitor has to be refreshed
and recharged to avoid data loss.
Dynamic RAM Cell Operation
In a DRAM cell, the storage capacitor will discharge in around 4-15ms. Refreshing the
capacitor by reading or sensing the value on bit line, amplifying it, and placing it back on
to the bit line is required. The need to refresh the DRAM cell complicates the DRAM
system design.
For details, refer to Chapter 7 of the text book.
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Table of Contents:
  1. Computer Architecture, Organization and Design
  2. Foundations of Computer Architecture, RISC and CISC
  3. Measures of Performance SRC Features and Instruction Formats
  4. ISA, Instruction Formats, Coding and Hand Assembly
  5. Reverse Assembly, SRC in the form of RTL
  6. RTL to Describe the SRC, Register Transfer using Digital Logic Circuits
  7. Thinking Process for ISA Design
  8. Introduction to the ISA of the FALCON-A and Examples
  9. Behavioral Register Transfer Language for FALCON-A, The EAGLE
  10. The FALCON-E, Instruction Set Architecture Comparison
  11. CISC microprocessor:The Motorola MC68000, RISC Architecture:The SPARC
  12. Design Process, Uni-Bus implementation for the SRC, Structural RTL for the SRC instructions
  13. Structural RTL Description of the SRC and FALCON-A
  14. External FALCON-A CPU Interface
  15. Logic Design for the Uni-bus SRC, Control Signals Generation in SRC
  16. Control Unit, 2-Bus Implementation of the SRC Data Path
  17. 3-bus implementation for the SRC, Machine Exceptions, Reset
  18. SRC Exception Processing Mechanism, Pipelining, Pipeline Design
  19. Adapting SRC instructions for Pipelined, Control Signals
  20. SRC, RTL, Data Dependence Distance, Forwarding, Compiler Solution to Hazards
  21. Data Forwarding Hardware, Superscalar, VLIW Architecture
  22. Microprogramming, General Microcoded Controller, Horizontal and Vertical Schemes
  23. I/O Subsystems, Components, Memory Mapped vs Isolated, Serial and Parallel Transfers
  24. Designing Parallel Input Output Ports, SAD, NUXI, Address Decoder , Delay Interval
  25. Designing a Parallel Input Port, Memory Mapped Input Output Ports, wrap around, Data Bus Multiplexing
  26. Programmed Input Output for FALCON-A and SRC
  27. Programmed Input Output Driver for SRC, Input Output
  28. Comparison of Interrupt driven Input Output and Polling
  29. Preparing source files for FALSIM, FALCON-A assembly language techniques
  30. Nested Interrupts, Interrupt Mask, DMA
  31. Direct Memory Access - DMA
  32. Semiconductor Memory vs Hard Disk, Mechanical Delays and Flash Memory
  33. Hard Drive Technologies
  34. Arithmetic Logic Shift Unit - ALSU, Radix Conversion, Fixed Point Numbers
  35. Overflow, Implementations of the adder, Unsigned and Signed Multiplication
  36. NxN Crossbar Design for Barrel Rotator, IEEE Floating-Point, Addition, Subtraction, Multiplication, Division
  37. CPU to Memory Interface, Static RAM, One two Dimensional Memory Cells, Matrix and Tree Decoders
  38. Memory Modules, Read Only Memory, ROM, Cache
  39. Cache Organization and Functions, Cache Controller Logic, Cache Strategies
  40. Virtual Memory Organization
  41. DRAM, Pipelining, Pre-charging and Parallelism, Hit Rate and Miss Rate, Access Time, Cache
  42. Performance of I/O Subsystems, Server Utilization, Asynchronous I/O and operating system
  43. Difference between distributed computing and computer networks
  44. Physical Media, Shared Medium, Switched Medium, Network Topologies, Seven-layer OSI Model