Rhodes Chroma Polaris

Following up to my own note, if you just want to do button presses, then 
you won't have to do an 'open' first; rather, you can just do a 'send 
message' command.

To confirm that sysex can be received OK by the host, from the Polaris 
do a LF-C-12.  This should perform a "send main workspace program out 
over MIDI."  It will do this via a sysex message.

You'll see something like:

   190905  F0 08 01 4F
           30 30 38 35
           30 31
   190909  F0 08 01 57
           32 43 30 30
           30 30 46 34
           30 30 31 43
           30 30 30 30
           30 30 30 30
           38 30 43 38
           41 45 30 36
           43 38 31 37
           38 36 35 31
           30 30 30 30
           30 31 30 30
           41 30 30 31
           46 43 30 44
           30 35 46 38
           30 31 31 43
           38 30 46 46
           30 36 30 30
           30 39 31 38
           30 30 30 30
           30 31 30 36
           30 30 30 30
           31 38 30 36
           30 32 37 35
           31 46
   190947  F0 08 01 53
           31 45 30 30
           37 46 30 30
           F7

Using the MIDI Implementation manual to decode the stream will give you 
a good felling for how the Polaris decodes/encodes sysex.

Of this dump, the last portion is the most interesting for your original 
question.  It has:

   190947  F0 08 01 53
           31 45 30 30
           37 46 30 30
           F7

Decoding the stream we have:

F0 08 01 = start of sysex, fender ID, channel # (in my case, the MIDI 
base channel was '2').

The Polaris uses ASCII strings to represent data - so for the first 
message we have:

 53 31 45 30 30 37 46 30 30 F7

0x53 = ASCII "S" = Send Message.

A 'send' has the following format:

   Sssiimmoo

Where S = ASCII for 'stream'
ss = stream number
ii = instrument number
mm = message
oo = operand

For this example, stream number = 1E (instrument stream)
instrument number = 00
Message = 7F
Operand = 00

In your case where you'd like to change the value of a switch, you'd to 
'send' to a stream.  Stream 16 is the panel stream.

So that would be:

F0 08 01 53 31 36 30 30 30 43 30 31 F7

Where:

53 = ASCII for "S"
31 36 = stream number "16"
30 30 = instrument number 00 (ignored)
30 43 = "0C" = 'switch press' command
30 31 = "01" = switch #1

So sending this command should 'press' switch #1 (The sequencer 'stop' 
button).  Changing the switch number (the last two bytes) will allow you 
to press any/all buttons on the Polaris.

A similar syntax can be used for slider moves.

Be sure to let us know how you make out.

David