Memory organization of
8051 Microcontroller
The
applications of microcontroller are more. Hence knowledge about interfacing
devices to the microcontroller and expanding of microcontroller memory is very
important. Memories like SRAM, EPROM, EEPROM are interfaced to microcontroller
to enhance capabilities of 8051.
1.Program
memory:
Program memory
accessed through EA pin. In program memory two categories takes place:
a)If EA is high, internal program memory is
accessed to 0FFFH memory location and external program memory accessed from
1000H to FFFFH memory locations.
b)If EA is low, only external program memory
accessed from 0000H to FFFFH memory locations.
2.Data
memory:
Data memory is used to
store the memory in the registers each of 64k bytes size, to access the data
memory instruction MOVX is used. Data memory is of two types Internal and
external.
i)Internal
data memory:
The internal data memory
consists of 256 bytes, these are divided into two parts:
00H-FFH for internal data RAM (128 bytes)
80H-FFH for special function registers (128 bytes)
2.External
data memory:
The 8051 gives the
facility to interface external RAM and ROM. External RAM is accessed by DPTR
and up to 64KB of RAM can be interfaced. External data memory interfacing is of
two types i.e. RAM and ROM interfacing.
i)RAM
interfacing:
The interfacing of memory chip
with microcontroller has some regulations to follow:
a)The memory data bus is directly connected to
memory chip data pins
b)Control signal connection
RD(Read Memory) connected to OE
(Output Enable)
WR(Write Memory) connected to
WE(Write Enable)
* The memory
chip consists of Chipset (CS) and Chip enable (CE) address lines varies based
on memory capacity chip should inbuilt with control signals, data lines. The accessing
of memory is done when chip is activated.
Example: Interfacing 4KB RAM
Let address chip is 3000H to 3FFF
ii)
ROM Interfacing:
In many systems the
on chip ROM of 8051 is not sufficient, so 8031 chip is used, it is a ROM less
version of 8051 which allows program size to be large as 64K bytes.
EA Pin: To
Indicate the program code stored in microcontroller on chip ROM, EA pin is
connected to Vcc, to indicate program code is stored in ROM EA pin is connected
to ground.
madharchod
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