Serial baud rate vs. high speed CAN

Question

The bottleneck in my current app is the serial writes at 115200, to a custom device.  The program dramatically improves in speed as the baud rate is increases.  If i remove the serial write and read, the program loop time improves from 100 to 2000htz 
The device also has a CAN interface.  Im debating trying to use the NI CAN interaface card to see if there are improvments in speed but want to get an opinoin first since this will require considerable reprogramming.  The can card appears to be just two serial ports but yet, accoring to specs, appears faster.
http://zone.ni.com/devzone/cda/tut/p/id/2732
Its difficult to try to compare serial and can speeds. CAN is up to 1mbits a sec while 115200 is measuring baud.  After considerable reserach to compare the two, i still am having difficulty. Im not sure these comparisions are even valid as Im more instrested in in sending one charcter and then recieving it rather than contual streaming of data whch is what these rates measure.

Answer 1

  This is a custom servotube powered by an amplifier.  The servo has a renishaw encoder for 1um resolution. The application requires reading the position of the renishaw encoder every iteration.  This positional information is then logged into the data.  The position is independent of the feedback loop but it is important for the research. The feedback loop itself is determined by a strain gauge and 9237 module which compute loading forces of the servotube, and this is converted to analog output value via pid and then sent via an ni analog output module to the differential input on the amplifier.  The differential inputs on the amplifier will create a current (I) for the servotube value based on the voltage it receives.
 The bottleneck only has to do with the serial port.  Reading the serial port can be accomplished with the serial or can interface.  Using the serial port, the commands to get the position and then read receive it back, can occur at a rate of around 350 iterations a second at the highest baud, 115200. This 350 iterations is if there is nothing else in the loop other than visa read and write of the serial port with no delays. Its the best case scenario and when the additional code is in place, we are getting more like 100 iterations a second. 
So the baud rate speed dosent seem to apply?  It is really a delay in the send and receive each time the communication is initiated?  That is why the can interface might be better?    Programming the NI can card seems a little tricky and i want to be sure it will offer improvement before jumping into this task. 
Maybe there is a chip or something NI has to read the position of the reinshaw on the available NI AD cards we have on the system.?  It would then reduce the bottneck?
Message Edited by Biosolutions on 10-15-2009 07:47 AM