Ch. 7
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Transcript of Ch. 7
Ch. 7
Memory and Programmable Logic
Memory and Programmable Logic
Random-Access MemoryMemory DecodingError Detection and CorrectionRead-Only MemoryProgrammable Logic ArrayProgrammable Array LogicSequential Programmable Devices
Memory
Memory – A device to which binary information is transferred
for storage.Type of memory
– random access memory , RAM– read-only memory, ROM
Write operation– Storing new information into memory
Read operation– Transferring the stored information out of memory
RAM
RAM– The time it takes to transfer information to or from
any desired random location is always the same
Storage unit–byte– byte : 8 bits
– Length of a word : multiple of 8 bits
– word : represent a number, an instruction, alphanumeric character
Capacity of memory–total number of bytes
Block diagram of memory unit
k address lines :select one particular word
read, write : specify the direction of transfer
n data input line :provide the information to be stored in memoryn data output line :supplying the information coming out of memory
Capacity of memory
Range of in memory size– 210~232 words
bytes– K=210 、 M=220 、 G=230 。– 64K=216 、 2M=221 、 4G=232 。
Memory 1K x 16– 10 bits address , 16 bits in each word
Determine the no. of bits for address
mk 2 k: no. of address bitsm: total number of words
Control inputs to memory chip
memory enable read/write memory
operation 0 x None 1 0 Write to select
word 1 1 read from
selectd word
Memory cycle timing waveforms
access time– the time required to select a word and read it
cycle time– the time required to complete a write cycle
access time 、 cycle time– equal to a fixed number of CPU clock
See Fig. 7-4
Types of memory
The mode of access of a memory– RAM-volatile
• Static RAM(SRAM)– internal latch – easier to used and shorter read and write time
• Dynamic RAM(DRAM) – electric charges on capacitor– less power consumption– larger storage capacity
– ROM-nonvolatile • Read/write time depend on the distance between
the magnetic reader/writer and the data
Memory Decoding
Decoder – select the memory word specified by the input
address
2-dimensional coincident decoding is a more efficient decoding scheme for large memories
Memory cell
One bit memory cell
4X4 RAM
Coincident Decoding- two-dimensional selection scheme
Decoder with k input and 2k output requires 2k AND gates with k input
k input decoder can be implemented by two k/2 input decoders with one for column and another for row
e.g., 10×1024 decoder can be implemented by two 5×32 decoders
Example for two-dimensional decoder
Address multiplexing64K-word memory
Read-Only Memory
ROM : permanent binary information is stored
k input, n output ROM
ROM
No data inputIntegrated circuit ROM have one or more
enable inputSometimes come with three-state outputs
to facilitate the construction of large arrays of ROM
Internal logic of 32X8 ROM
ROM truth table
Table 7-3 32×8 ROM truth table 輸入 輸出
I4 I3 I2 I1 I0 A7 A6 A5 A4 A3 A2 A1 A0
0 0 0 0 0 1 0 1 1 0 1 1 0
0 0 0 0 1 0 0 0 1 1 1 0 1
0 0 0 1 0 1 1 0 0 0 1 0 1
0 0 0 1 1 1 0 1 1 0 0 1 0 . . .
.
.
.
1 1 1 0 0 0 0 0 0 1 0 0 1
1 1 1 0 1 1 1 1 0 0 0 1 0
1 1 1 1 0 0 1 0 0 1 0 1 0
1 1 1 1 1
0 0 1 1 0 0 1 1
Programmomg the ROM according to Taable 7-3
× denote a connection in place of a dot used for permanent connection
Example 7-1
輸入 輸出
A2 A1 A0 B5 B4 B3 B2 B1 B0
十進位
0 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 1 1
0 1 0 0 0 0 1 0 0 4
0 1 1 0 0 1 0 0 1 9
1 0 0 0 1 0 0 0 0 16
1 0 1 0 1 1 0 0 1 25
1 1 0 1 0 0 1 0 0 36
1 1 1
1 1 0 0 0 1
49
Design a combinational circuit with 3-input using a ROM.Output = square(input)
ROM implementation of Example 7-1
Types of ROMs
The required path in a ROM may be programmed in four different ways. – mask programming (mask ROM)
• Mask is done by Fab. company during the last fabrication
• Customer must fill out the truth table
• High cost
– programmable read-only memory(PROM)• allows users to program in Lab.
• the program is irreversible
Types of ROMs
– Erasable PROM(EPROM)• by ultraviolet light
– electrically-erasable PROM(EEPROM or E²PROM) ,
• by electrical signal • can be erased without removing it from tis socket
Types of PLD (Programmable Logic Device)
Programmable Logic Array (PLA)
similar to PROM does not provide full decoding and does
not generate all the mintermsdecoder is replaced by an array of AND
gate
PLA with 3 inputs, 4 product terms, and two outputs
PLA Programming Table
PLA Programming Table consists of three sections
– 1st, list the product terms numerically
– 2nd, specify the required path between inputs and AND gates
– 3rd, specifies the paths between the AND and OR gates
outputs
inputs (T) (C) Product
term A B C F1 F2
BA 1 1 0 - 1 -
AC 2 1 - 1 1 1
BC 3 - 1 1 - 1
CBA 4 0 1 0
1 -
Example 7-2
Implement the following two Boolean functions with a PLA:
Simplified by K-map :
)7,6,5,0(),,(
)4,2,1,0(),,(
2
1
CBAF
CBAF
CBAACABF
BCACABF
2
1 )(
Solution of Example 7-2