Specifications

mikroElektronika | Free Online Book | PIC Microcontrollers | Chapter 1: PIC16F887 Microcontroller - Device Overview
Table 1-1 cont. Pin Assignment
Central Processor Unit (CPU)
I’m not going to bore you with the operation of the CPU at this stage, however it is important to state that the CPU is
manufactured with in RISC technology an important factor when deciding which microprocessor to use.
RISC Reduced Instruction Set Computer, gives the PIC16F887 two great advantages:
● The CPU can recognizes only 35 simple instructions (In order to program some other microcontrollers it is necessary
to know more than 200 instructions by heart).
● The execution time is the same for all instructions except two and lasts 4 clock cycles (oscillator frequency is
stabilized by a quartz crystal). The Jump and Branch instructions execution time is 2 clock cycles. It means that if
the microcontroller’s operating speed is 20MHz, execution time of each instruc tion will be 200nS, i.e. the program
will be executed at the speed of 5 million instructions per second!
Fig. 1-4 CPU Memory
Memory
This microcontroller has three types of memory- ROM, RAM and EEPROM. All of them will be separately discussed since
each has specific functions, features and organization.
ROM Memory
ROM memory is used to permanently save the program being executed. This is why it is often called “program memory”.
The PIC16F887 has 8Kb of ROM (in total of 8192 locations). Since this ROM is made with FLASH technology, its contents can
be changed by providing a special programming voltage (13V).
Anyway, there is no need to explain it in detail because it is automatically performed by means of a special program on
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