Serial Servo Controller communication problem

[ikd]

Hello,<br /><br />I am trying to implement simple control of a Pololu serial controller: <a href="http://www.pololu.com/catalog/product/727/resources" target="_blank">http://www.pololu.com/catalog/product/727/resources</a><br /><br />There are two commands that I am interested in:<br />1. Set speed is achieved by sending a sequence of 5 bytes: 0x80 0x01 0x01 0x00 speed_byte<br />2. Set absolute position is achieved by sending the following sequence: 0x80 0x01 0x04 0x00 pos_byte1 pos_byte2<br /><br />For example speed_byte = 0x10, pos_byte1 = 0x10, pos_byte2 = 0x00.<br /><br />I have attached a sreenshot of my VI.<br /><br />The problem is with first byte sequence write (setting velocity). It fails, but then the second command is executed well (with default speed parameter).<br />When I try to run only the set absolute position command (right after setting properties of port) it also fails. Looks like some portions of the sequence are corrupted.<br /><br />I am using the latest version of NI VISA.<br /><br />Could anyone give a clue of what is happening?<br /><br />

<b>Upd: I have tried to used a serial port debugger, and checked that two programs (Pololu serial transmitter which works correctly and my program) give exactly the same output to the COM-port.<b />

[Mellroth]

QUOTE (ikd @ Oct 21 2008, 10:59 AM)

...The problem is with first byte sequence write (setting velocity). It fails, but then the second command is executed well (with default speed parameter).

When I try to run only the set absolute position command (right after setting properties of port) it also fails...

Sounds like a timing issue.

Try to put a msWait node after you have configured the serial port, i.e. don't send your commands directly after the config.

/J

[ikd]

QUOTE (JFM @ Oct 21 2008, 03:04 PM)

Try to put a msWait node after you have configured the serial port

I've tried to put a wait after port configuration, but it didn't help

[Dan Press]

Mine looks slightly different. This is from some old code, but it does work.

[jdunham]

I think VISA Serial defaults to a text-oriented mode, where EOL chars are sent automatically at the end of each write. You should be using more VISA properties to make sure all those features are turned off.