Newbie question about Serin and loops

NewJerseyTN

If I have a serin in a loop does execution stop at the serin until a byte is on the pin the serin is looking at?· What I'm hoping is that it doesn't and it just continues to the rest of the code.

Bruce Bates

NewJersey TN -

Execution does stop until one of two things occurs. One is that the SERIN criteria is satisfied, or two, the timeout period has expired.

Satisfying the SERIN critera may mean matching particular specified characters, or accepting a specified number of digits or an EOD indication (i.e. carraige return).

Regards,

Bruce Bates

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allanlane5

Yes, the BS2 is a single-tasking machine. So it ONLY recieves data while sitting in a SERIN command, and while it's sitting in the SERIN command it's not doing anything else. There's NO buffering, in other words. So you do have to do something to allow the BS2 to 'miss' bytes and still be able to 'synchronize' with a sender.

On the good side, it can SERIN on any I/O pin. On the bad side, only one at a time.

NewJerseyTN

Well, that sounds like I might be ok then if the timeout is short enough. Basically what I'm wanting to do is this:

Get a byte from my PocketPC
If a byte was sent set a varible to that byte
depending on the varible move a servo to a setpostion + an additional small random number
get a new random number
loop back to getting a byte from the PocketPC

I don't want the stamp to sit waiting for data from the PocketPC. I want it to go on updating that random number and making small movements in the servo. But when data is there I want it to get it.

allanlane5

The servo needs to be updated every 20 mSec. So you can spend that 20 mSec in the 'Wait' timeout for the SERIN. You might want to send the byte from your PocketPC more than once, though.

NewJerseyTN

allanlane5,

Well, that's why I have the varible that I'm setting the BYTE from serin to. As long as that varible isn't updated by the serin it should stay the same and the servo will get an updated signal in the loop after the serin call. Also I'm thinking of getting the serial servo controler from Parallax anyway. I believe it keeps a constant signal to the servo. I've looked at the help again on serin and the timeout parameter looks like just what the doctor ordered.

allanlane5

I think when a SERIN does a timeout, it zero's the returned variable. This doesn't have to be a problem if you have a spare byte of variable space to store the 'last good' servo position. Also, probably 'zero' is not a 'good value' to set the servo to, so you can detect this 'bad' value.

NewJerseyTN

allanlane5,

Yeah, a returned zero will be fine because the data I'm going to get from the PocketPC isn't going to be positional, more of an action to take. So I'm going to have the PocketPC send a character for "forward" and let the basic stamp handle what the right position for "forward" is.