PC to Controller Board communication

[umka]

I have done a search to see if I could find any relevant info but unfortunately found nothing on ccs.

I want to build an autonomous robot that uses two dc motors (CCP1 and CCP2) and has several inputs and outputs and communicates with a PC via a hard wire. The pc will have a program written in VB6 to control the robot.

Question 1: Would it make sense to use a device like a PIC18F4550 that has built in USB so I can emulate a serial connection to perform the pc to robot control communication or is there a better or simpler way to do this.

Question 2: I was thinking of sending strings like “Left,fwd,60”- for left motor forwards at 60%, “Output,12,1”- for output high pin 12 and “Input,3”- to check the input on pin 3. Is this a good way of doing it? Was thinking would read in the string then copy the characters up to the , into 3 different buffers and then compare them to set string to enter different control loops. Is there code that does this already that I didn’t find or a similar way that I could use?

Cheers for the help

[ckielstra]

Question 1: USB or RS232
There is no general answer for the on being better than the other, it depends a lot on how you are going to use the device.
USB is a bit more difficult to program but with the example programs provided by CCS this shouldn't be a problem. Most of the newer PC's don't have an RS232 connector, especially true for laptops. Another advantage of USB is that it can provide power to your electronics.
But... a disadvantage of USB is the limited cable length of maximum 5m. (link). Using the maximum of 5 USB hubs you could extend this up to 30m but this is not very practical.

RS232 is easy to program and can be used over a distance up to 15m at a data rate of 256kbs. With good quality cables and lower data rates the maximum distance can be increased.

Question 2: Commands as strings?
Sending the commands as human readable strings has the advantage that on the transmitting PC you can use a standard terminal program like Hyperterm to enter the commands. Also easy for debugging. A disadvantage is that on the receiving PIC you will have to parse the commands into something understandable by the processor. This includes all kind of user input errors (small or capital letters, extra spaces, empty lines, too large values, etc.).
The alternative is to send the commands as binary codes, for example: 1 2 60
Where 1 is the left motor, 2 means forward and 60 is the speed.
Not easy to read for humans but a lot easier for the PIC, you can even add a checksum to detect communication errors. On the PC side this requires a dedicated program with a nice user interface for translating the user commands to the binary format.

For the string command parser several example programs have been posted in this forum, here are just a few examples:
Ttelmah: http://www.ccsinfo.com/forum/viewtopic.php?t=28159
Mark (C18 compiler): http://www.ccsinfo.com/forum/viewtopic.php?t=28159
CCS: the ex_fat.c example program

[umka]

Cheers for the advice ckielstra. Have got it working and working well at that I think.