CompactRISC is a family of
instruction set architecture
In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
s from
National Semiconductor
National Semiconductor was an American semiconductor manufacturer which specialized in analog devices and subsystems, formerly with headquarters in Santa Clara, California. The company produced power management integrated circuits, display dr ...
.
The architectures are designed according to
reduced instruction set computing
In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set compu ...
principles, and are mainly used in
microcontroller
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs ( processor cores) along with memory and programmabl ...
s.
The subarchitectures of this family are the 16-bit CR16 and CR16C and the 32-bit CRX.
CR16 architectures
Features of CR16 family: compact implementations (less than 1 mm
2 with
250 nm), addressing of 2 MB (2), frequencies up to 66 MHz, hardware multiplier for 16-bit integers.
[
It has complex instructions such as bit manipulation, saving/restoring and push/pop of several registers with single command.][
CR16 has 16 general purpose registers of 16 bits, and address registers of 21 bits wide. There are 8 special registers: program counter, interrupt stack pointer ISP, interrupt vector address register INTBASE, status register PSR, configuration register and 3 debug registers. Status register implements flags: C, T, L, F, Z, N, E, P, I.][
Instructions are encoded in two-address form in several formats, usually they have 16-bit encoding, but there are two formats for medium immediate instructions with length of 32-bit. Typical opcode length is 4 bits (bits 9–12 of most encoding types. Basic encoding formats are: Register-to-Register, Short 5-bit immediate value to Register, Medium immediate of 16-bit value to Register (32-bit encoding), Load/Store relative with short 5-bit displacement (2-bit opcode), Load/Store relative with medium 18-bit displacement (32-bit encoding, 2-bit opcode).][ CR16C comes with a different opcode encoding format, has 23–32-bit-wide address registers and provides two 32-bit general purpose registers.
CR16 implements traps and interrupts. Implementations of CR16 has three-stage pipeline: fetch, decode, execute.][
]
CR16 products
CR16 was used in several National Semiconductor microcontrollers, and since 2001 integrated microcontrollers were available having built-in flash memory. Since 2007 CR16-based IP was available to licensing
References
External links
National Semiconductor Embedded Microcontrollers
(CR16 and COP8
The National Semiconductor COP8 is an 8-bit CISC core microcontroller. COP8 is an enhancement to the earlier COP400 4-bit microcontroller family. COP8 main features are:
* Large amount of I/O pins
* Up to 32 KB of Flash memory/ ROM for co ...
)
CompactRISC Core Architecture
page on National Semiconductor website (archived copy from 2007)
CR16B Programmer’s Reference Manual
National Semiconductor, 1997
Microcontrollers
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