STMicroelectronics STM8 Architecture Overview

atomar — Wed, 10 Jul 2013 06:39:16 GMT

Current Revision posted to Documents by atomar on 7/10/2013 6:39:16 AM

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Overview

The STM8 core is an evolution of the industry‑standard ST7 core. It has been significantly improved to reach 1.6 cycles per instruction and up to 24 MHz clock frequency.

The 8-bit STM8 Core is designed for high code efficiency. It contains 6 internal registers, 20 addressing modes and 80 instructions. The 6 internal registers include two 16-bit Index registers, an 8-bit Accumulator, a 24-bit Program Counter, a 16-bit Stack Pointer and an 8-bit Condition Code register. The two Index registers X and Y enable Indexed Addressing modes with or without offset, along with read-modify-write type data manipulation. These registers simplify branching routines and data/arrays modifications.

The 24-bit Program Counter is able to address up to 16-Mbyte of RAM, ROM or Flash memory. The 16-bit Stack Pointer provides access to a 64K-level Stack. The Core also includes a Condition Code register providing 7 Condition flags that indicate the result of the last instruction executed.

The 20 Addressing modes, including Indirect Relative and Indexed addressing, allow sophisticated branching routines or CASE-type functions. The Indexed Indirect Addressing mode, for instance, permits look-up tables to be located anywhere in the address space, thus enabling very flexible programming and compact C-based code. The stack pointer relative addressing mode permits optimized C compiler stack model for local variables and parameter passing.

The Instruction Set is 8-bit oriented with a 2-byte average instruction size. This Instruction Set offers, in addition to standard data movement and logic/arithmetic functions, 8-bit by 8-bit multiplication, 16-bit by 8-bit and 16-bit by 16-bit division, bit manipulation, data transfer between Stack and Accumulator (Push / Pop) with direct stack access, as well as data transfer using the X and Y registers or direct memory-to-memory transfers.

The number of Interrupt vectors can vary up to 32, and the interrupt priority level may be managed by software providing hardware controlled nested capability. Some peripherals include Direct Memory Access (DMA) between serial interfaces and memory. Support for slow memories allows easy external code execution through serial or parallel interface (ROMLESS products for instance).

The STM8 has a high energy-efficient architecture, based on a Harvard architecture and pipelined execution. A 32-bit wide program memory bus allows most of the instructions to be fetched in 1 CPU cycle. Moreover, as the average instruction length is 2 bytes, this allows for a reduction in the power consumption by only accessing the program memory half of the time, on average. The pipelined execution allowed the execution time to be minimized, ensuring high system performance, when needed, together with the possibility to reduce the overall energy consumption, by using different power saving operating modes. Power-saving can be managed under program control by placing the device in SLOW, WAIT, SLOW-WAIT, ACTIVE-HALT or HALT mode.

Key Features

The key features of the STM8 core are:

Harvard architecture
16‑bit index registers and stack pointer
32‑bit memory interface and 3‑stage pipeline
Extended instruction set
Enhanced stack pointer operations
Move instruction for fast data transfer
Hardware division (16 / 8)
Faster multiplication (8 x 8)
8‑bit signed arithmetic support
Advanced addressing modes including indexed addressing
Statistically optimized instruction tables

Applications

Mainstream
- Industrial and Consumer
- Robust and reliable
Automotive
Ultra Low Power
Touch sensing

Video

www.youtube.com/watch

Technical Documents

Learning Center

Type	Description
Product Brief	STMicroelectronics: Product Brief for STM8 8-bit MCU family

Kits & Evaluation Modules

STM8 8-bit MCUs

Part Number	Core Architecture	Silicon Family	Description
STM8/128-EVALSTM8/128-EVAL	STM8	STM8S2xx	Evaluation Board for STM8S series with STM8S208MB MCU
STM8L101-EVALSTM8L101-EVAL	STM8	STM8L1/L2	Evaluation Board for STM8L101 MCUs
STM8L-DISCOVERYSTM8L-DISCOVERY	STM8	STM8L	Discovery kit for STM8L series with STM8L152C6 MCU
STM8S-DISCOVERYSTM8S-DISCOVERY	STM8	STM8S	Discovery Kit for STM8S Series with STM8S105C6 MCU

Tags: stm8, stmicroelectronics