Discovery: The More Things Change...

This week's post was going to be an introduction to ST Microelectronics' STMF4Discovery board, leading into a protracted series of posts dealing with the tools involved, the processor, peripherals, and on-board chips.

When I went to Digikey to get the latest price for the board, I found out that there was none available. What? How can I write a series of posts when nobody can follow along? Noooooo!

The STM32F4Discovery board is a ARM Cortex-M4F development board from ST. It's uses the STM32F407 processor, which is big enough for a lot of projects, but cheap enough to be a good alternative to an Arduino. But where did the board go?

ST replaced it with a new version (version MB997D), but also changed the name to STM32F407G-DISC1, which is why I couldn't find it on Digikey. From the change notes on the schematic, it appears that the difference between the old board and the new board, beyond the silkscreen changes, is that the processor on the debugger module has simply been changed to a version with 128K of Flash memory rather than 64K.

The recent development boards from ST are mbed enabled and the change to this board seem to be to support mbed. What does that mean? The debugging module on the board gives you a USB debugger identical to the ST-Link module. With mbed, the debugger module also shows up with a USB disk drive and a USB serial port. You can drag and drop your executable onto the disk drive and it will get blown into the processor without a Flash loader program like OpenOCD.

The USB serial port is interesting addition. Previously I would have to stab an FTDI serial to USB module into the bus pins to talk to your board's UART. Now, in theory, the serial port comes out of the debugger module USB connector and shows up on your PC as a virtual serial port. This is super convenient, if ST actually hooked a UART to the debugger processor. In the board manual they show how to solder bodge wires between the bus pins and the debugger processor. I expect that in the next version this bodge will be turned into traces.

I have checked to see if the new mbed firmware will fit in the older versions of the STMF4Discovery boards (version MB997C), no unfortunately it won't work.


This post is part of a series. Please see the other posts here.


 Old and new - or is it new and old?

Old and new - or is it new and old?