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Driver for NXP PCA9685 LED/PWM (Servo) controller
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Rookie
Joined: Thu Sep 20, 2012 2:13 pm Posts: 1 
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 Driver for NXP PCA9685 LED/PWM (Servo) controllerThank you for your work on this.
(I accidentally posted this question to the topic "RELEASED: 3RD PARTY ROBOTC DRIVER SUITE V2.7" so please ignore it there.) I am struggling to write a Mindstorms NXT driver for the NXP PCA9685 LED/PWM (Servo) controller I2C chip. I am using the Adafruit Server Controller module. Adafruit provides a driver in c for Arduino processors to control this board, so I am using that to help understand how to write one for NXT. The main thing I need to figure out is, how do the RobotC I2C calls compare with the wire.h calls? In wire.h these calls are used to write to the PCA9685: Wire.beginTransmission(_i2caddr); Wire.write(addr); Wire.write(d); Wire.endTransmission(); where: _i2caddr = the bus address of the PCA9685 addr = Specifies what address within the PCA9685 to write the next value to d = the value to write to the address given by addr. To set the position of a servo, you would do the above steps 4 times to set the on, off, high and low bytes. In Robotc, would this be a way to accomplish basically the same thing? Note that the array passed to writetoI2C() has 3 values in it. Does each value in the array get sent sequentially? bool PCA9685sendBytes(tSensors link, ubyte _byte) { memset(PCA9685_I2CRequest, 0, sizeof(tByteArray)); PCA9685_I2CRequest[0] = 3; // Message size PCA9685_I2CRequest[1] = _i2caddr; // I2C Address PCA9685_I2CRequest[2] = _addr; // PCA9685 control-register address PCA9685_I2CRequest[3] = _byte; return writeI2C(link, PCA9685_I2CRequest, 0); } Thanks again! |
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| Thu Sep 20, 2012 6:26 pm |
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Moderator   Joined: Wed Mar 05, 2008 8:14 am Posts: 2864 Location: Rotterdam, The Netherlands
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Re: Driver for NXP PCA9685 LED/PWM (Servo) controller Hi kahnfu,
It's fine, I deleted it and split this one off from the other thread.
Other than being able to do I2C, not a whole lot. The names are very different and you don't have to deal with the stop and start conditions yourself. The firmware takes care of that stuff for you.
Yeah, almost. The first byte is the actual size of the transmission, 3 bytes in this case (address, register and value to be sent to register).
This code looks fine to me. Please note that for the 3.0 beta 1 driver suite, I've changed some of the internal I2C functions, but it would be super easy to modify, you'll see. _________________ | Some people, when confronted with a problem, think, "I know, I'll use threads," | and then two they hav erpoblesms. (@nedbat) | My Blog: I'd Rather Be Building Robots | ROBOTC 3rd Party Driver Suite: [Project Page] |
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| Sat Sep 22, 2012 1:05 am |
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