Out in Front: September 12, 1996

When you think RISC, you generally think of a 32-bit processor. Furthermore, in the world of 8-bit µCs, you generally think of well-established architectures. Atmel is breaking tradition by introducing its 8-bit RISC architecture called the AVR. AVR RISC properties include a 16-bit, fixed-length instruction, a load/store architecture, 32 general-purpose registers, and an instruction executed on every clock accomplished by prefetching an instruction during the previous instruction execution. As part of the evolution toward the use of higher level languages, AVR includes special instructions that support C programming. Although Atmel sells many 8051s, the company claims that AVR is 10 times faster than the 8051, which requires four to 12 clocks per instruction.

AVR's 32 registers constitute the architecture's fast-access RISC register file and are in direct connection with the processor's ALU. The register file is dual-mapped and can be addressed as part of the on-chip SRAM. Some µCs in the AVR product family feature a hardware multiplier in the arithmetic portion of the ALU. AVR uses a Harvard-style architecture and directly addresses up to 8 Mbytes of program memory and 8 Mbytes of data memory.

Low-end versions of AVR, with no onboard RAM, have a limited four-level-deep hardware stack dedicated to subroutines and interrupts. On parts with onboard RAM, there is a RAM-based rather than a hardware stack. The I/O memory space contains 64 addresses for CPU peripheral functions, such as control registers, timer/ counter, A/D converters, and other I/O functions.

Atmel offers a free Windows-based, absolute assembler. In October, IAR Systems (San Francisco) will offer a more powerful, relocatable assembler as well as an ANSI-compliant C compiler. Atmel also offers an emulator for the AVR.

The first AVR product is the AT90S1200. It features 64 bytes of EEPROM, 1 kbyte of flash memory, an SPI, 15 programmable I/O lines, one 8-bit timer/ counter, a watchdog timer, an on-chip analog comparator, and 2.7V operation. It sells for around $2 (1000).

—by Markus Levy

Atmel Corp, San Jose, CA. (408) 441-0311, http://www.atmel.com.