Digital Design: RAM, Address and Data Buses, Memory Decoding, Semiconductor Memories Part - II

Chapter 17

RAM, Address and Data Buses, Memory Decoding, Semiconductor Memories

Ch17L2- "Digital Principles and Design", Raj Kamal, Pearson Education, 2006 2

Lesson 2

Common Bus OrganizationCommon Bus Organization


Outline

•• Tristate buffer and inputTristate buffer and input--out buffer out buffer on common lineson common lines

• Bus• Organization of registers on common

bus• Data bus and address buses


Tristate 4-bit Buffer Register on common Lines

RegisterOut-Enable(Read)

Commondata Lines


Tristate 4-bit Input/Output (IO)Buffer on common data Lines

Out-Enable(Read)

Common data Lines

IO Buffer

Load-Enable(Write)


Tristate 4-bits of Memory Cell array on common data Lines

Out-Enable(Read)

Common data Lines

Cell-array

Load-Enable(Write)


Read and write control signals

• Read control signal enables reading through data lines

• Write control signal enables writing (storing/loading) through data lines


Common Set of lines• A Common data Lines function for

Reading lines (output lines) when Read = 0; Write = 1 Common data Lines function for Writing (input lines) when control signals Read = 1; Write = 0

• Using tristate IO buffer register, we can write into that and read from that using four lines D0, D1, D2 and D3, and read and write signals to buffer


Outline

• Tristate buffer and input-out buffer on common lines

•• BusBus• Organization of registers on common

bus• Data bus and address buses


Data Bus and control signals

• Common Set of data lines, which can be used by several registers, memory units or ICs provided each one for each bit has a tristate buffer each and there is a common read control and another common write control signals to buffer


Address Bus

• Common Set of address lines, which can be used to select using a decoder only one of the several registers, memory units or ICs provided only one has distinct address


Bus• Data Bus facilitates connecting many

unit on common set of data lines, each unit is using it when addressed

• Address Bus facilitates selecting one of many unit through decoder in between

• Address bus has lines , which are common for decoders for all the units


Outline


• Bus•• Organization of registers on Organization of registers on

common buscommon bus• Data bus and address buses


Input/Output (IO) Registersorganised on common select line

and data lines

Out-Enable(Read)

Common 4 data Lines(Data Bus)

Four IO BufferRegisters

Load-Enable(Write)

2 to 4 lines decoder

Common 2address Lines(Address Bus)

4

2


Outline


• Bus• Organization of registers on common

bus•• Data and address busesData and address buses


Data Bus

• Data bus is bi-direction as it can function as output lines during read and as input lines during write to a buffer register or cell array of memory

• 8-bit Data bus connects 8-bit register or memory-cell array or IO buffer


Address Bus

• Address bus is unidirectional, originating and is from reading or writing unit or system to the decoders. Decoder select only one data byte for read or write from or to 8-bit data bus

• Address of 10 bits addresses one of 210

bytes for or from 8-bit data bus


Summary


• All bits are accessed through tristate buffers

• Common set of lines, which carry data for write and carry data for read connect all memory cell arrays or registers or buffers. Lines are called data bus


• Read control signal enables tristate buffers to read a memory cell arrays or registers or buffer by an external system or unit

• Write control signal enables tristate buffers to write into a memory cell arrays or registers or buffer by an external system or unit


• Common set of lines, which carry address for a memory cell array or register or buffer address to be selected for write or read

• Lines are input to decoder, which selects just one addressed cell array or register or buffer at an instance

• Lines to decoder for selecting addressed unit are called address bus


End of Lesson 2

Common Bus OrganizationCommon Bus Organization


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