[En-Nut-Discussion] Device driver using TWI and 1-wire

[Harald Kipp]

Lars,

>Ok, I'll start working on something and we'll see how it turns out. By the 
>way the device I am working with is a LIS3L02DS 3-axis accelerometer from 
>ST. It generates new measurements in 280Hz. This requires a bandwidth of 
>1960 bytes/s on the TWI interface. Is there a known maximum bandwidth 
>supported for the TWI driver?

Never measured it, but I used it with 115200 bps (14400 B/s)
without difficulties.


>Regarding the battery backup, did you mean that one should let the state 
>machine handle the communication with the ds2760?

Not sure about this one. My personal rule of thumb on
state machines in general is: They make complicated things
look simple and simple things look complicated.

The state machine I'd been referring too was a hardware
implementation of the ISA protocol...simplified.

>I am having some trouble figuring out the best way to mount the battery 
>backup on the Ethernut board. I would prefer if it can be placed 
>underneath the main board leaving the J3 connector open. If anyone has 
>ideas about the design, please let me know !

J3? J3 is the RS232 connector. May be you meant JP3.
I'm afraid, but like with most jumpers its position
is not fixed and may not fit on later Ethernut versions.
Only JP2 and JP3 on Ethernut 1 are safe, because a few
custom boards use these to attach to the RS232 line.

I recommend the expansion port and feed 5V to the
Ethernut. For example, you can solder a cable on the
expansion port and use a cable connector on the
battery backup board. When using the DC supply, you
need about 6.2V. On JP3 it's even 7.6V absolute minimum.

Btw. as far as I understood the data sheet, the
LM1086 doesn't require any protection diode and
should have no problem with 5V on its input.

Harald