Wednesday, October 17, 2012

Introducing the STMicro F3 Family of ARM Cortex-M4 Microcontrollers

Last year STMicro introduced the STM32 F4 family of high-performance ARM Cortex-M4 microcontrollers.  They are now launching the F3 series, a lower cost family of Cortex-M4 microcontrollers.

What is Cortex-M4?  It is the 32bit ARM microcontroller heart of these single chip computers.  It differs from the Cortex-M3 and Cortex-M0 in that it has an added floating point unit (FPU) to perform faster floating point calculations.  It also has instructions intended to speed up digital signal processing (DSP) and digital signal control applications such as single-cycle multiply-accumulate (MAC) instructions, saturating arithmetic instructions, and SIMD (single instruction, multiple data) instructions to speed data processing.  Details on the Cortex–M4 can be found on the ARM web site Cortex-M4 page (click on the Specifications and Technology tabs).

The F3 family is intended for DSP/control applications that do not require the large memories or the interface options of the F4 family.  The Cortex-M4 core provides the same DSP and single-precision floating point instructions as found in the F4 series.  However, the F3 reduces the cost by removing memory and some of the communications interfaces of the F4’s (such as Ethernet) while adding some new analog features. 

The new analog features include 5 megasample-per-second ADCs, 16-bit sigma-delta ADCs, programmable gain amplifiers, comparators, and three DACs on some versions.  Some models have four ADCs with up to 39 input channels.

Discovery-F3 Module

A new discovery board is being distributed to support the new device.  It provides a STM32F303VC microcontroller with 256k of Flash memory and 48k RAM.  The module has the same two 50-pin DIL headers as the Discovery-F4 board, but the pinout is slightly different.  The built-in STlinkV2 SWD programmer/debugger allows code to be downloaded and debugged without additional hardware.  Also provided on the Discovery-F3 board are the L3GD20 3-axis digital gyroscope and LSM303DLHC 6-axis geomagnetic module.  Details on the Discovery-F3 can be found on the STMicro web site Discovery-F3 page.  To get a Discovery-F3 module in North America, attend one of the STM32 F3 North American Seminars in November and December 2012.

Kornak Technologies is developing a baseboard for the Discovery-F3 that breaks out the connectors to individual headers to speed the assembly of your prototype system.

STM32 F3 and F4 Family Comparison

The following table contrasts the similarities and differences between the F3 and F4 families.

STM32 F3 Family,
Analog with DSP
STM32 F4 Family,
High-Performance DSP, with Connectivity and Crypto
ARM Core
MCU Frequency
72 MHz
168 MHz
Floating Point Unit
Single precision FPU
IEEE 754 compliant
Single precision FPU
IEEE 754 compliant
48 to 100 pins
64 to 176 pins
Flash Memory
64k to 256k
512k to 1024k
16 to 48k (some with parity checking)
9 to 39 channels, 1 to 4 ADCs
13 to 24 channels, 3 ADCs
16bit sigma-delta ADCs
Yes, on STM32F37x devices and STM32F38x devices, 1 to 3
Yes, 1 to 3
Yes, 2
PGA (programmable gain amp)
Yes, up to 4
Analog Comparators
Yes, up to 7
Ethernet (10/100 Mbps)
Yes, on STMF4x7 devices
FSMC Ext Memory Interface
Yes, on 100pin or more devices
3 or 5 USARTs
4 USARTs + 2 UARTs
2 or 3 SPI
2 I2C
3 I2C
Yes, 1 USB FS
Yes, 2, USB OTG (1 FS + 1 HS)
Crypto Processor
Yes, on STM32F41x devices
Random Number Generator
CRC Calculation Unit
Camera Interface
Yes, on STMF4x7 devices

To see which chips offer which mix of features, please download and view these Excel spreadsheets.  I find it helpful to color the cells of the features I am interested in and sort on the key parameter.

STM32 F3 Family - MCUs with DSP and Analog Functions
Kornak-STMicro STM32-F3 Product List 2012-10-15.xls

STM32 F4 Family - High-Performance MCUs with DSP for Connectivity and Crypto
Kornak-STMicro STM32-F4 Product List 2012-10-15.xls

Please send any comments or corrections to