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As I mention in another post I am trying to find a microcontroller that can handle a Lynxmotion hexapod. Unfortunately I am stuck with hobby servos so I would like a controller with 18 ADC pins and to generate 18 PWM signals (in hardware as opposed to bit banging). Looking through the datasheet for the ATxmega128A1 it would seem to have what I need but I'm not confident I am interpreting the document correctly.

The way I read it the chip has 8 16-bit timers. Each of 4 of the timers have 4 comparators and each of the other 4 have two for a total of 24 total pins that can generate PWM. It also appears to have 2 ADC with 4 result registers each and 4 way muxing for a total of 32 pins with ADC. The pins for the timers and ADC all appear to be on different ports so there is no clashing amongst them. My question to you is, is this interpretation correct?

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DaemonMaker
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  • Take a look at section 30.2. It has tables of pin multiplexed functions. In particular, there are only 16 physical pins capable of ADC functions, and these are multiplexed with analog comparators/external references, so the actual number of pins you can use for ADC inputs might actually be less. – helloworld922 Jul 08 '13 at 19:19

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There are external I/O expanders with PWM.
PCA9671 for example, has an I2C interface.
OpenServo. It's an aftermarket retrofit board for a commercial R/C servo, which accepts commands via I2C. (available on sparkfun)

P.S. It's not an uncommon misconception that a hobby servos really require hardware PWM on μC side. Servos need to be updated with a pulse every 20ms. A whole lot of servos can be updated from a single timer interrupt service routine (ISR).

Nick Alexeev
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  • Thanks @Nick. I understand that I don't need hardware PWM but for my other, unspecified goals, it would be nice. :D – DaemonMaker Jul 08 '13 at 19:23
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A colleague pointed out that each of port A and B only have 8 pins each. This can be seen by referencing Figure 3-1 of the datasheet. Unfortunately it means that there are in fact only 16 pins with ADC, not 32 as I had previously thought. Similarly, since the timers are on ports C, D, E, and F, and also are limited to 8 pins there must only be 16 pins capable of PWM generation.

DaemonMaker
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