Memory Interfacing

• Connecting memory with the microprocessor• The address bus, data bus, control signal are

need to connect with MP• Address bus to send address• Data bus to read and write the data• Control signal to specify read and write

operation

Generation of control Signal

• When IO/ =0 and =0 , signal is generated

• When IO/ =0 and =0 signal is generated

• When IO/ =1 and =0 signal is generated

• When IO/ =1 and =0 signal is generated

• The address in the bus select particular location in memory

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Interface Four locations

Interface Eight location

• To interface Eight memory location how many address lines are needed ?

• Three address line • That is address decoder is three to eight

decoder

• How many address lines are need to interface 64 KB of memory

• 2 16= 64 KB• So 16 address lines are needed• A0 to A15 address lines are directly connected

to memory • Only one location is selected by internal

decoder for each address

A15

A0

Gnd

64 KB

• How many address lines are need to interface 32 KB of memory

• 2 15= 32 KB• So 15 address lines are needed• If I left 16 th address line and use 15 add line

only• What will happened?

Gnd

A0

A14

First location add is 0000(H)Last Location add is 7FFF(H)

= 8000= 8001

FFFF

•Same memory is selected for the range of 8000 (H) to FFFF(H)•First location address is 8000(H)•Last location address is FFFF(H)

• So all the address line should be included in address decoding

• The address lines needed for the memory location are connected directly

• Remaining all address lines should be used to generate chip select signal

A14

A0

A15

•For address range oooo to 7FFF, A15 is “0” so chip is not selected•No location will be selected

= 8000= 8001

FFFF

•For address range 8000 to FFFF A15 is “1” so chip is selected• Address range of the memory is 8000 t0 FFFF

What is the address range of bellow memory

A15

A0

A14

• For address range oooo to 7FFF A15 is “0” so chip is selected

• For address range 8000 to FFFF A15 is “1” so chip is not selected

• Address range of the memory is 0000 t0 77FFF

Interface 1 KB memory

• To Interface 1KB memory 10 address lines are needed

• So connect 10 address lines to memory directly

• Remaining 6 address lines should be decoded externally to generate chip select signal

Interface 1KB memory

Address range of 1 KB memory

0 0 0 0 0 0 03FF