{"id":21,"date":"2015-11-21T18:50:35","date_gmt":"2015-11-21T18:50:35","guid":{"rendered":"http:\/\/martinelectronics.co.uk\/wp\/?p=21"},"modified":"2015-11-21T18:53:38","modified_gmt":"2015-11-21T18:53:38","slug":"introducing-the-picmicro-from-microchip-technology","status":"publish","type":"post","link":"http:\/\/martinelectronics.co.uk\/wp\/?p=21","title":{"rendered":"Introducing the PICmicro from Microchip technology"},"content":{"rendered":"

PIC is a family of RISC microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument’s Microelectronics Division.<\/p>\n

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).<\/p>\n

\"General<\/a>
General Instrument’s PIC1655<\/figcaption><\/figure>\n

In 1985 General Instruments spun off their microelectronics division, and the new ownership cancelled almost everything \u2014 which by this time was mostly out-of-date.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, LCD drivers, 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).<\/p>\n

\"Various<\/a>
Various PIC microcontrollers<\/figcaption><\/figure>\n

 <\/p>\n

Writing Code for PICs<\/p>\n

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.<\/p>\n

Third parties make C and BASIC language 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 or C30 which disables some optimiser features after a timeout period. Open-source compilers for the C, Pascal, JAL, and for the Forth programming language, PicForth, have also been released.<\/p>\n

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, OS\/2 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.<\/p>\n

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 (12V) is present on the Vpp\/MCLR pin. Low voltage programming allows for the elimination of the extra voltage rail in the programmer but comes at the cost of an IO pin and can therefore be disabled (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 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.<\/p>\n

Many of the higher end flash based PICs can also 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.<\/p>\n

There are many programmers\/debuggers available directly from Microchip:<\/span><\/p>\n