Memory Allocation. Three kinds of memory Fixed memory Stack memory Heap memory.
Memory
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Memory Section 7.2
description
Memory. Section 7.2. Types of Memories. Definitions Write: store new information into memory Read: transfer stored information out of memory R andom- A ccess M emory (RAM) Can read and write Read-Only-Memory (ROM) Read only. Interesting Facts. - PowerPoint PPT Presentation
Transcript of Memory
Memory
Section 7.2
Types of Memories
• Definitions–Write: store new information into
memory– Read: transfer stored information out of
memory
• Random-Access Memory (RAM)– Can read and write
• Read-Only-Memory (ROM)– Read only
Interesting Facts
• Interesting fact of RAM: the time it takes to transfer information to or from any desired random location is always the same
• A word =a group of bits– A group of 8 bits is called a byte.–
Two Types of RAM
• Static RAM (SRAM): Stored information remains valid as long as power is applied to the unit.
• Dynamic RAM (DRAM): Stores binary information in the form of electric charges on capacitor provided inside the chip by MOS transistors.
74LS189 RAM
64 bits=16 4-bits words.
Block Diagram of a Memory Unit
74LS189 RAM
[A3,A2,A1,A0]=address inputs[D3,D2,D1,D0]=data inputs[S3,S2,S1,S0]=outputsME,WE control the direction of transferVCC=powerGND=ground
Logic Diagram memory cell
Each word is enabled by the 4-input AND
Write →Read
Logic Diagram memory cell
Each word is enabled by the 4-input AND
Switch Characteristics
Switching Time Waveforms
17 nS 23 nS
-7 nS for address-14 nS for data
A negative hold time means that the address/data can change before the rising edge of WE because the thereis internal delay through the chip.
Write (ME=0, WE=0)
0
0
10
11
11
D1
D2D3D4 [hi Z?]
READ (ME=0, WE=1)
1
0
01
Complement of data stored
HOLD (ME=1, WE=X)
X
1
0Hi-Z output
Memory Description in Verilog
memory depth: 64 words
word length4-bits
Need 6 bits address for 26=64 words.
Enable ReadWrite
1 1 Read
1 0 Write
0 X Hi-Z
