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PICmicro Memory

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PICmicro chips have three separate areas of memory - program memory (Flash), user variable memory (RAM), and EEPROM. These names give strong hints as to the purpose of the areas! For the 18 pin 16F84 the following graphic illustrates the organisation of the memory:

The program memory is used to store the program! In most PICmicro chips, such as the 16F1937, this memory uses 'Flash' technology. This means that it can be programmed and cleared many times. Older PICmicro's use PROM for the program memory and many of these can be programmed only once.

The data memory is used to store data! Part of this uses RAM and part uses EEPROM. The EEPROM allows us to preserve important data even if the power supply to the system is switched off. For example, suppose that the PICmicro is part of a temperature controller that keeps an incubator at a set temperature. It might make sense to store the required temperature value in EEPROM so that we do not have to enter it into the system every time we switch the incubator on.

The 16F84 illustrated is a relatively small device. In the 16F1937 there are 8192 words of program memory (each word has 13 bits), 512 bytes of user RAM and 256 bytes of EEPROM.

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