Swap your old ARM microcontroller for a Cortex-M3
Monday 20 June 2011 10:40
Guest columnist Dirk Jansen, product marketing manager for MSC Vertriebs, says if you want to ungrade your ARM7 MCU why not reach for a Cortex-M3 microcontroller, it can be function- and pin-compatible.
Atmel’s new AM3S and SAM3N flash Cortex-M3 microcontrollers are compatible with the earlier SAM7S flash ARM7 series and can offer more powerful peripherals, more performance and bigger memories.
The SAM7S microcontroller family, which is based on the ARM7TDMI core, was introduced as the first single-chip ARM7 family as long ago as 2004. It has up to 512k flash with up to 64k SRAM, boot ROM, with peripherals such as a full-speed USB device, an eight-channel 10-bit ADC, a PWM unit and three 16-bit timers.
The microcontroller was packaged in LQFP/QFN 48- and 64-pin housings.
The SAM7S had no external bus interface.
This was then introduced later with the SAM7SE family.
For the next generation of ARM products, the Cortex-M3 based SAM3 flash families, Atmel licensed the Cortex-M3 Rev 2 with MPU (not in the SAM3N) and full debug system without ETM.
Atmel went over to 128-bit embedded flash with a pre-fetch unit to increase the execution performance from the flash, for example up to about 86DMIPs (SAM3U at 96MHz clocking). A SAM7S achieved a maximum of 38DMIPs in thumb mode at 55MHz and code execution from the 32-bit flash.
The power consumption at low clock rates has been reduced. SAM3 MCUs work “battery-compatibly” within the voltage range of 1.62 to 3.6V; only the ADC requires at least 2V analogue supply.
Eight- and 16-bit wide external bus interfaces were also integrated into the 100+-pin derivates on which static memory such as flash, SRAM, memory mapped IO (LCD, FPGA) or NAND flash (ECC is integrated into the SAM3) can be operated.
For those who need multi-phase PWM with downtime generator for motors or power inverters motor-compatible PWM units can produce up to 4+4 phases with DMA and emergency stop support in the SAM3. The DMA-supported parallel I/O capture mode, which permits parallel import from I/O pins via DMA, is completely new.
This means that camera modules can be read out and the picture data written to RAM while “bypassing” the CPU.
There is on-chip power management, and integrated RC oscillators – with the help of the PLLs – can generate the full system clock. Battery-supported RTC timers and RC oscillators now even permit the implementation of clock functions. Power consumption in active and standby modes has been reduced by about 40%.
Thanks to fast RC oscillators, wake-up periods have been reduced to a few micro-seconds.
Larger memories will soon make possible fundamental updates to your SAM7 firmware to add features or protocol stacks. If the flash grows, the SRAM has to follow. Atmel will integrate up to 128KB of SRAM.
With an eye on the many SAM7S applications in the market, Atmel has presented two SAM3 families which are pin- and function-compatible to the SAM7S families and permit a simple upgrade to Cortex-M.
The SAM3S family is to be regarded as a possible upgrade, as significantly more peripherals, timers and also new features have been integrated here. So anyone who needs the computing power of a Cortex-M3 but can manage without several peripherals can downgrade to the USB-free SAM3N family if necessary. SAM3N is also pin-compatible to the SAM7S family and to all SAM3S variants.