Today, I thought my Akai EWI USB had broken. Turned out to just me forgetting which mode I had set it in…

But while I had the thing taken apart, I learned some interesting pieces of information about the design.

It a 3.3 volt ARM7 chip, the STR751FR0. Here’s the link to STMicroelectronics’ website: http://www.st.com/web/catalog/mmc/FM141/SC1714/LN1106/PF147084

The 2 pin header next to the chip allows the chip to enter “SystemMemory Boot Mode”. Putting a jumper on these pins and booting the chip will tie pin 4 to Vdd (high) and should tell the chip to start listening for programming commands on the UART0_RX and UART0_TX lines…

At least, that’s what it says in the data sheet. I wouldn’t recommend doing this unless you know what you’re doing… Sending bad serial data down to a chip could probably kill the programmed firmware… Go read the programming PDF’s first.

The 6 pin header seems to be the programming header itself. Following are the pinouts I was able to trace. Just because I wasn’t able to figure out the rest of the pins doesn’t mean they aren’t connected…:

1 -> Ground
2 -> ??
3 -> ?? (Something to do with pin P2.10?)
4 -> Pin 19, UART0_RX
5 -> Pin 18, UART0_TX
6 -> ??

Also, the unpopulated button is connected to pin 15, which is labeled NJTRST. After a google search I found this: “NJTRST does not reset the chip, just portions of the JTAG chain/circuit.”

What’s weird is that it seems like JTAG isn’t actually hooked up. The JTAG peripheral is hooked up to pins 11-15 by default… but from what I can see on the board, it doesn’t look like any traces are running away from them…

This is a >2 layer board though… so maybe they’re just off somewhere else on the board? Maybe they used pogopins for JTAG?

Anyways, I’m not gonna dig in and start trying to reprogram the thing. I don’t really know the ARM7 dev toolchain and learning it to write a new version of the firmware is probably not worth the time.

Besides, capacitive sensing has come a long way… and this board is doing all the cap sensing stuff the old school way… With a more modern MCU, and a 3D printer, you could build your own EWI…

Now to put this back together again…