PIC microcontroller

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PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division.
PICs are popular with developers and hobbyists alike due to their low cost, wide availability, large user base, extensive collection of application notes, availability of low cost or free development tools, and serial programming (and re-programming with flash memory) capability.
Microchip recently announced the shipment of its five billionth PIC processor.

Data Space (RAM)

PICs have a set of register files that function as general purpose ram, special purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series, and all PIC devices have some banking mechanism to extend the addressing to additional memory. Later series of devices feature move instructions which can cover the whole addressable space, independent of the selected bank. In earlier devices (ie. the baseline and mid-range cores), any register move had to be through the accumulator.

To synthesize indirect addressing, a "file select register" (FSR) and "indirect register" (INDF) are used: A read or write to INDF will be to the memory pointed to by FSR. Later devices extended this concept with post and pre increment/decrement for greater efficiency in accessing sequentially stored data. This also allows FSR to be treated like a stack pointer.
External data memory is not directly addressable except in some high pin count PIC18 devices.

Device Programmers

Devices called "programmers" are traditionally used to get program code into the target PIC. Most PICs that Microchip currently sell feature ICSP (In Circuit Serial Programming) and/or LVP (Low Voltage Programming) capabilities, allowing the PIC to be programmed while it is sitting in the target circuit. ICSP programming is performed using two pins, clock and data, while a high voltage (12V) is present on the Vpp/MCLR pin. Low voltage programming dispenses with the high voltage, but reserves exclusive use of an I/O pin and can therefore be disabled to recover the pin for other uses (once disabled it can only be re-enabled using high voltage programming).

There are many programmers for PIC microcontrollers, ranging from the extremely simple designs which rely on ICSP to allow direct download of code from a host computer, to intelligent programmers that can verify the device at several supply voltages. Many of these complex programmers use a pre-programmed PIC themselves to send the programming commands to the PIC that is to be programmed. The intelligent type of programmer is needed to program earlier PIC models (mostly EPROM type) which do not support in-circuit programming.

Many of the higher end flash based PICs can also self-program (write to their own program memory). Demo boards are available with a small bootloader factory programmed that can be used to load user programs over an interface such as RS-232 or USB, thus obviating the need for a programmer device. Alternatively there is bootloader firmware available that the user can load onto the PIC using ICSP. The advantages of a bootloader over ICSP is the far superior programming speeds, immediate program execution following programming, and the ability to both debug and program using the same cable.

Microchip Programmers

There are many programmers/debuggers available directly from Microchip.
Microchip Programmers (as of 10/2005)
* PICStart Plus (RS232 serial interface) : intelligent.
* Promate II (RS232 serial interface) : intelligent.
* MPLAB PM3 (RS232 serial and USB interface)
* ICD2 (RS232 serial and USB interface) : ICSP programming only (primary function is debugging).
* PICKit 1 (USB interface)
* PICKit 2 (USB interface)

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