Peripherals

AN2945

6/18

Doc ID 15468

2

Peripherals

The MCU peripherals (also called IPs) are another example of the ST MCU consistency

across the 8- and 32-bit product lines: most of the basic IPs have been defined and

structured to be portable from one product family to the other. This was done by adapting

simple, yet effective, 8-bit peripherals to the 32-bit world. It brings the benefits of cost- and

power-effective, easy to understand resources, which are complemented at system level by

wider busses and a DMA controller when higher performance is needed. Once the working

principle of a peripheral is understood, it is applicable to both the STM8S and STM32

families, thus speeding up transition between devices.

Figure 1 shows a simplified representation of a digital peripheral.

Figure 1.

Digital peripheral’s internal structure

The peripheral can be partitioned into two main blocks. First, a kernel that contains the state

machines, counters and any kind of combinatorial or sequential logic necessary to perform

tasks that do not need the processor, such as low-communication layers, analog front-end

management or timing-driven functions. If necessary, the kernel is connected to the external

world via MCU ports. The external connection may consist of a few I/Os or complex busses.

Second, the peripheral is initialized and controlled by the application through registers

connected to an internal bus shared with the other MCU resources. In 8-bit microcontrollers,

the processor directly writes to and reads from registers, whereas in 32-bit products, register

read and write operations usually go through a bridge. The main difference between the two

families, however, lies in the internal bus specification the peripheral has to comply with.

This explains why STM8S and STM32 devices are able to share peripherals: these are

based on the same kernel, and are only tailored to the two different bus interfaces. ARM

processors and peripherals comply with the AMBA bus specification, with a 32-bit databus,

Bus interface

& registers

IP kernel

I/Os

ai15955