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Kinetis, PIT gated transfert activation

Question asked by tatali faku on Aug 12, 2017
Latest reply on Aug 14, 2017 by xiangjun.rong



I am using a MK66FX1M0VMD18 and I am trying to perform DMA transfer using PIT gated transfer activation but I found no answer anywhere to my question.


My DMA transfers work perfectly when I use PIT-only activation. It also works when using FTM channel only.


According to Kinetis Quick Reference User Guide (Rev 3), trigger mode, figure 7.4, In PIT gated mode, channel is activated only if both PIT trigger and Peripherial Request are HIGH.


In my case, I use a PIT triggering at ~20MHz and a FTM channel running at 31Khz with a PWM duty of 87%. With this configuration, PIT signal goes HIGH multiple times during one FTM channel signal HIGH. I expected to obtain multiple channel activations, roughly 87% of 20,000,000 PIT triggers followed by 13% without any trigger.


My problem is it is not what I obtained. I obtain a transfer running at the same speed as the FTM channel (31KHz). I assumed a logical AND between PIT signal and Peripherial request signal due to Pit-only transfer activation figure but I may be wrong. It is like the channel cannot be re-activated until both signals goes LOW.


My question is simple. In PIT gated transfer activation mode, if the PIT trigger signal  goes HIGH 2 times and Peripherial Request signal is HIGH during these 2 times (without ever going LOW), is the channel activated 1 or 2 times ?