Hi there;

I've been doing some analysis of the AVR Butterfly to see what
usefulness it might have as a robotics controller and thought I would
share the results with everyone. Everything I found I got from the
schematics in the butterfly's userguide I downloaded from Atmel.
It was a pretty brief look so if anyone finds any booboos let me know
and I will post a correction.

The big thing I was looking for was useful I/O pins, especially
I/O pins with analog to digital converters or pulse width modulation
channels.

Two 8-bit ports (with associated I/O pins) have connectors that we
can get at: port B and port D.  Unfortunately, those ports are
shared with lots of other (but useful) stuff.

All four PWM channels are either shared with the navigation switch or
the piezo speaker. We are stuck with the speaker unless we disconnect
it. If we want to use the remaining PWM channels we just have to make
sure that no stupid humans fiddle with the button at the same time.
I would add an external switch that is monitored by the AVR through
one of the other usable ports and determines whether the motors are
enabled or not.  You could end up with a short if the PWM channels are
in use and the user starts navigating with the switch. 

The rest of port B is shared with the ISP port (which isn't a big
deal as long as we use those pins for output only), the navigation
switch or the dataflash.

Port D also has a connecter but those pins are shared with the LCD.
According to the schematic they are connected but I am not sure if the
LCD actually uses them.  If they are used by the LCD then that entire
port will be unusable unless the LCD is disabled.

However, all is not lost. There are 4 pins on the JTAG port that are
useful (PF4-7). They are also ADC channels. That's cool.

The USI interface is also open for us (pe4-6).   The UART pins,
however, have voltage converters attached going to j406.  This
converts the serial voltages to the usual +12/-12 so we can hook it up
to a PC.  If we want to run that to a low voltage serial device we
would need to keep the high voltages in mind.

The dataflash is tres cool.  It's accessible through the SPI interface
(you must disable the AVR's SPI interface before you can do that but
getting back from that state could be challenging) and, of course,
you can get at it through the AVR.  It has 4 megabits of data or 512
kliobytes.  You could, say, have the butterfly record the temperature
every 60 seconds for an entire year.  You will overwrite the
tunes that comes with the butterfly if you do that.

Overall, we don't have a huge number of ports to work with but with
clever design it can still be quite useful.

Here is a little table that shows the pin -> device/connector mappings.

Port refers to the AVR I/O port as described in the atmega169 docs.

Purpose is the pin's function.  SegXX refers to the attached LCD segment.

Connector refers to the holes on the butterfly that we can solder headers
into.

Device refers to the device on the butterfly.

Note that some I/O pins have multiple uses.  i.e. they are hooked up to
a port and a device. 

There are 7 groups of locations where we can solder in headers.  Below is
a little table that describes the header group (jXXXX) and what it does.

j400 port b
j401 port d
j402 jtag/adc
j403 isp
j404 battery clip
j405 usi (universal serial interface)
j406 uart *works through a voltage converter
j407 voltage reader

    port  purpose            connector  devices     alternate connector
--------------------------------------------------------------------------------
01        LCDCAP
02  pe0   rxd/pcint0         J406*
03  pe1   txd/pcint1         J406*
04  pe2   xck/ain0/pcint2               nav switch
05  pe3   ain1/pcint3                   nav switch
06  pe4   usck/scl/pcint4    j405
07  pe5   d1/sda/pcint5      j405
08  pe6   d0/pcint6          j405
09  pe7   clk0/pcint7
10  pb0   ss/pcint8          j400       flash
11  pb1   sck/pcint8         j400       flash       j403-x-ISP
12  pb2   mosi/pcint9        j400       flash       j403-x-ISP
13  pb3   miso/pcint10       j400       flash       j403-x-ISP
14  pb4   oc0a/pcint12       j400       nav switch
15  pb5   oc1a/pcint13       j400       piezo
16  pb6   oc1b/pcint14       j400       nav switch

    port  purpose            connector  devices     alternate connector
-------------------------------------------------------------------------------
17  pb7   oca2/pcint15       j400       nav switch
18  pg3   t1/seg24
19  pg4   t0/seg23
20        reset
21        vcc
22        gnd
23        tosc2/xtal2
24        tosc1/xtal1
25  pd0   icp1/seg22         j401
26  pd1   int0/seg21         j401
27  pd2   seg20              j401
28  pd3   seg19              j401
29  pd4   seg18              j401
30  pd5   seg17              j401
31  pd6   seg16              j401
32  pd7   seg15              j401

    port  purpose            connector  devices     alternate connector
-------------------------------------------------------------------------------
33  pg0   seg14
34  pg1   seg13
35  pc0   seg12
36  pc1   seg11
37  pc2   seg10
38  pc3   seg9
39  pc4   seg8
40  pc5   seg7
41  pc6   seg6
42  pc7   seg5
43  pg2   seg4
44  pa7   seg3
45  pa6   seg2
46  pa5   seg1
47  pa4   seg0
48  pa3   com3

    port  purpose            connector  devices     alternate connector
-------------------------------------------------------------------------------
49  pa2   com2
50  pa1   com1
51  pa0   com0
52        vcc
53        gnd
54  pf7   adc7/td1           j402-9-jtag
55  pf6   adc6/td0           j402-3-jtag
56  pf5   adc5/tms           j402-5-jtag
57  pf4   adc4/tck           j402-1-jtag
58  pf3   adc3
59  pf2   adc2                          light sensor
60  pf1   adc1                          voltage reader
61  pf0   adc0                          temperature
62        aref
63        gnd
64        avcc
-------------------------------------------------------------------------------