September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Microchip PICmicro family
	View block diagram

The register-based PICmicro family comprises the eight-pin PIC12C5xx/67xx, the baseline PIC16C5x, the midrange PIC16Cxx, and the high-end PIC17Cxx. These controllers employ a modified Harvard, RISC architecture that supports various-width instruction words. The datapaths are 8 bits wide, and the instruction widths are 12, 14, and 16 bits wide for the PIC16C5x/PIC12C5xx, PIC12C67xx/PIC16Cxx, and PIC17Cxx, respectively. Variable instruction-bus widths allow all the devices to fetch instructions in a word and execute most instructions in one pipelined cycle.

A new PIC18C1xx architecture is upward-compatible with Microchip's other architectures and offers new features, such as 16-bit-wide instructions, 68 instructions, as much as 2M words of program memory, and as much as 4 kbytes of data memory. The PIC18C1xx has a 32-entry-deep hardware stack—up from eight and 16 deep on other family members. The PIC16C1xxx also includes a software stack to better support high-level languages, such as C. The PIC18C1xx has improved interrupt capability with a fast-interrupt mode for external or internal interrupts. The fast interrupt performs hardware-context saves using shadow registers. A bit in the return-instruction operation code tells the CPU whether to return from an interrupt using the shadow or regular stack.

PICmicros are available with one-time-programmable EPROM, flash, EEPROM, and program ROM. Only the PIC17Cxx supports external memory via a multiplexed, 16-bit-address, 8-bit-data external bus. The PIC16Cxx and PIC17Cxx architectures support instruction words as large as 8 and 64 kbytes, respectively. Multiple register sets allow fast context switching. The PIC16C5x lacks interrupt support, so it handles external-event interrupts via polling; the PIC16Cxx and PIC17Cxx devices have as many as 12 and 18 interrupt sources, respectively.

Scenix Semiconductor produces the SX family, designed to be PIC-compatible but capable of operating at higher frequencies. This family implements a four-stage fetch, decode, execute, and write-back pipeline and can execute one instruction per cycle. The higher performance of the SX allows it to implement peripherals, such as dual-tone multiple-frequency and FSK generators, in software.

Power management: Low-power sleep mode reduces power consumption to only transistor leakage. In this mode, the PIC devices maintain RAM and register contents while all clocks are stopped. All devices operate at 32 kHz to save power.

Special instructions: PICmicro bit-manipulation instructions are bit set, clear, and test. Math functions include add, subtract, increment, and decrement. PIC16Cxx and 17Cxx have a decrement-and-skip-on-0 instruction. The PIC17Cxx adds a bit toggle, a multiply, and code-saving compare-and-skip instructions. The PIC17Cxx also supports table instructions that move data into and out of program memory—typically constants—to registers for processing.

Special on-chip peripherals: The PIC16C9xx family (winner of EDN's 1997 Innovation of the Year award) contains an LCD controller that generates its voltage from a high-current, switched-capacitor charge pump. This charge pump, operating off a 3V supply voltage, uses four external capacitors as part of an analog sampling circuit that measures system losses and overcharges accordingly. The charge pump can generate as much as three times the supply voltage, resulting in improved display contrast independent of varying battery voltages. Some PIC devices contain a high-speed USART that supports a 1.25-Mbps asynchronous interface. Other features include internal brownout reset and an internal on-chip RC oscillator that is accurate to within 5% and frees I/O lines for other system functions.

Development tools: Microchip provides in-circuit emulators (ICEs), a development system, a device programmer, a development environment, a C compiler, a macro assembler, and fuzzy-logic-development software. Aisys (www.aisys-usa.com) offers MP-DriveWay, which allows you to automatically create the software to initialize and control the PIC's peripherals. In addition, more than 125 third-party developers offer development systems for the PICmicro architecture.

Microchip's PICmaster Universal ICE interfaces to Windows and includes an emulator-control pod, a target-specific emulator probe, a programmer, a PC host-interface card, and PC-host-emulation control. In addition, the development tool contains Microchip's MPLab development environment. Microchip offers a lower cost ICE for the PIC16C5x and PIC16Cxx devices. This ICE provides many breakpoints; single, multiple, and procedure steps; the ability to display and modify any register; user-selectable processor speeds via an oscillator module; context-sensitive help; and an RS-232C port.

The $199 PICstart development system supports all current and future PICmicro devices and features a development programmer allowing users to program user software.

Second sources: There are no second sources for the PICmicro family.

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