Broad Classification of different microcontroller chips could be as follows:
· Embedded (Self -Contained) 8 - bit Microcontroller
· 16 to 32 Microcontrollers
· Digital Signal Processors
Features of Modern Microcontrollers
· Built-in Monitor Program
· Built-in Program Memory
· Analog I/O
· Serial I/O
· Facility to Interface External Memory
Internal Structure of a Microcontroller
At times, a microcontroller can have external memory also (if there is no internal memory or extra memory interface is required). Early microcontrollers were manufactured using bipolar or NMOS technologies. Most modern microcontrollers are manufactured with CMOS technology, which leads to reduction in size and power loss. Current drawn by the IC is also reduced considerably from 10mA to a few micro Amperes in sleep mode(for a microcontroller running typically at a clock speed of 20MHz).
Harvard Architecture (Separate Program and Data Memory interfaces)
The same instruction (as shown under Princeton Architecture) would be executed as follows:
- Complete previous instruction
- Read the "Move Data to Accumulator" instruction
- Execute "Move Data to Accumulator" instruction
- Read next instruction
Hence each instruction is effectively executed in one instruction cycle, except for the ones that modify the content of the program counter. For example, the "jump" (or call) instructions takes 2 cycles. Thus, due to parallelism, Harvard architecture executes more instructions in a given time compared to Princeton Architecture.
In the 8051, the memory is organized logically into program memory and data memory separately. The program memory is read-only type; the data memory is organized as read-write memory. Again, both program and data memories can be within the chip or outside.
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