PIC microcontroller
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PIC, is a family of RISC microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division.
Microchip Technology does not use PIC as an acronym; in fact the brand name is PICmicro. It is generally regarded that PIC stands for Peripheral Interface Controller, although General Instruments' original acronym for the PIC1650 was "Programmable Intelligent Computer".
The original PIC was built to be used with GI's new 16-bit CPU, the CP1600. While generally a good CPU, the CP1600 had poor I/O performance, and the 8-bit PIC was developed in 1975 to improve performance of the overall system by offloading I/O tasks from the CPU. The PIC used simple microcode stored in ROM to perform its tasks, and although the term wasn't used at the time, it is a RISC design that runs one instruction per cycle (4 oscillator cycles).
In 1985 GI spun off their microelectronics division, and the new ownership cancelled almost everything — which by this time was mostly out-of-date. The PIC, however, was upgraded with EPROM to produce a programmable channel controller, and today a huge variety of PICs are available with various on-board peripherals (serial communication modules, UARTs, motor control kernels, etc.) and program memory from 512 words to 32k words and more (a "word" is one assembly language instruction, varying from 12, 14 or 16 bits depending on the specific PICmicro family).
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Coding for PICs
PICs use a RISC instruction set, which varies in length from about 35 instructions for the low-end PICs to about 70 instructions for the high-end PICs. The instruction set includes instructions to perform a variety of operations on the accumulator and a constant or the accumulator and a memory location, as well as for conditionally executing code and jumping/calling other parts of the program and returning from them, and specific hardware features like interrupts and one low-power mode called sleep. Microchip provides a freeware IDE package called MPLAB, that also includes a software simulator as well as an assembler.
Third parties make C compilers for PICs. Microchip also sells compilers for the high-end PICs ("C18" for the 18F series and "C30" for the dsPICs). They also make available for download a "student edition/demo" version of C18 which disables some optimiser features after a timeout period. Open-source compilers for the Pascal, JAL, and for the Forth programming language, PicForth, have also been released.
GPUTILS is an Open Source collection of tools, distributed under the GNU General Public License. GPUTILS includes an assembler and linker and works on Linux, Mac OS X, and Microsoft Windows. GPSIM is an Open Source simulator for the PIC microcontrollers featuring hardware modules that simulate specific devices that might be connected to them, like LCDs.
Programming PICs
Devices called "programmers" are traditionally used to get program code into the target PIC. Most PICs that Microchip sells nowadays have 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 the RB6 and RB7 pins for clock and data, while a high voltage is present on the /MCLR pin. There are many programmers for PIC microcontrollers, ranging from the extremely simple designs that rely on the communications software for taking care of all the communication details to complex designs that can verify the device at several supply voltages and can do much of the work in the hardware. Many of these complex programmers use a pre-programmed PIC themselves to send the programming commands to the PIC that is to be programmed.
Word Size
The word size of PICs is a source of much confusion. All PICs (except the dsPICs) handle data in 8-bit chunks, so they should be called 8-bit microcontrollers. But unlike most CPUs PICs use a Harvard architecture, so the size of an instruction can be different. In fact different PIC families uses different instruction sizes, which makes it a challenge to compare the code size of PICs to other microcontrollers. For example, say a microcontroller has 6144 bytes of program memory --- for a 12-bit PIC, this works out to 4096 words (or assembly instructions); for a 16-bit PIC, this is 3072 words.
Modern PICs
The old PROM and EPROM PICs are now gradually replaced by chips with Flash memory. Likewise the original 12-bit instruction set of the PIC1650 and its direct descendants has been superseded by 14-bit and 16-bit instruction sets. Microchip still sells OTP (one-time-programmable, or PROM) and UV-eraseable (EPROM) versions of most of its PICs for legacy support, or volume orders. It should be noted that the microchip website lists pics that are not electrically erasable as OTP despite the fact that UV erasable windowed versions of these chips can be ordered.
Features
Current PICs offer a wide range of built-in hardware, such as:
- Timers
- Synchronous/asynchronous serial transmission UARTs
- Analog-to-digital converters
- Voltage comparators
- Capture/Compare/PWM modules
- LCD Drivers
- I2C and SPI peripheral Bus Support
- Internal (software accessible) EEPROM memory
- Motor Control Kernels
- USB interfacing support
PICs on the Internet
PICs are well-documented on the Internet, mainly for two reasons. First, PICs were commonly used to defeat the security system of popular consumer products (pay-TV, PlayStation), which attracted the attention of crackers. Second the (now obsolete, see PIC16F84) PIC16C84 was the first widely available microcontroller that could easily be re-programmed by hobbyists.
PIC clones
Every now and then there are companies that offer cheap and/or enhanced PIC versions. Most seem to disappear quite soon. Ubicom (formerly Scenix) seems to avoid this fate and produces PIC clones that run much faster than the originals. OpenCores has a pic16f84 core written in Verilog.
Wireless PICs
The rfPIC microcontroller devices integrate the power of Microchip´s PICmicro devices with UHF wireless communication capabilities for low power RF applications. The devices offer small package outline and low external component count to fit the most space-constrained applications.
dsPICs (Digital Signalling PICs)
dsPICs are Microchip's newest family, which entered mass production in late 2004. These are Microchip's first inherent 16-bit (data) microcontrollers. They build on the PICs existing strengths by offering hardware MAC (multiply-accumulate), barrel shifting, bit reversion, (16x16)-bit multiplication and other digital signal processing operations.
8-bit PIC microcontroller product families
These links take you to product selection matrices at the manufacturer's site.
- PIC10 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1009&mid=10&lang=en&pageId=74)
- PIC12 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1001&mid=10&lang=en&pageId=74)
- PIC14 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1008&mid=10&lang=en&pageId=74)
- PIC16 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1002&mid=10&lang=en&pageId=74)
- PIC17 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1003&mid=10&lang=en&pageId=74)
- PIC18 (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1004&mid=10&lang=en&pageId=74)
Commonly used PICs
- PIC12C508/509 (Small 8-pin package, internal oscillator, popular in small designs)
- PIC16F84 (Generally considered obsolete, but impossible to kill and very popular)
- PIC16F84A (Nice upgrade to above, some versions do 20MhZ, 1:1 compatible)
- PIC12F629/675
- PIC16F628
- The PIC16F87X family (The PIC16F84's big brothers, with lots of inbuilt hardware. Quite common in hobby projects.)
- PIC18F452
See also
External links
- Microchip (http://www.microchip.com)
- Ubicom (http://www.ubicom.com)
- PIClist (PIC mailing list and info site) (http://www.piclist.com)
- Page with links to the original PIC1650 documents (http://www.idcomm.com/personal/ottosen)
- GPUTILS (http://gputils.sourceforge.net) (Open Source assembler and linker)
- GNUPIC (http://www.gnupic.org) (site with many Open Source PIC development resources)
- YaPIDE (http://www.mtoussaint.de/yapide.html) (An IDE and simulator for the PIC 16F628 released under the GPL-2 license)
- PicForth (http://www.rfc1149.net/devel/picforth)
- PIC Discussion Group (http://www.embeddedrelated.com/groups/piclist/1.php)
- SDCC (http://sdcc.sourceforge.net/) Small Device C Compiler can compile for PIC
- HOODMICRO Development Kit (http://www.k9spud.com/hoodmicro/) providing a combination PIC Programmer and PIC Protoboard with plastic enclosure.da:PIC mikrocontroller