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Forum Index : Microcontroller and PC projects : PWM...explain to me like I'm a 5 year-old 
| Author | Message | ||||
| PhenixRising Guru  Joined: 07/11/2023 Location: United KingdomPosts: 857 |
What precludes us from having a PWM like this? It has been explained before but it went straight over my head   |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6776 |
The PWM system uses hardware modules on the RP chip. It's not all handled in firmware. The RP has a number of "slices", 8 for the RP2040 and 12 for the RP2350. Each "slice" has a single clock divider, a single 16-bit counter and two outputs. Each "slice" can be enabled or disabled in software. Although all GPIO pins can be used for PWM they have to be in pairs, one pair for each "slice". Thus the RP2350B, which has 48 GPIO pins, has 12 "slices" and can have 24 simultaneous PWM pins arranged as 12 pairs. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
Ah, I should have been more specific. In the above table, it shows the option of 19.531KHz with 12bits resolution. This is great for driving H-Bridge + motor. But we only have ~10bits, no matter the frequency, right? |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9104 |
I don't know where this has come from. The number of bits depends on frequency. Above CPU speed / 65536 it will start to drop but below that it will be between 15 and 16 bits.  You can see here that with a CPU frequency of 252MHz I have just under 8 bits of resolution at 1MHz but nearly 16 at 1KHz MM.INFO(PWM COUNT slice) gives the total counts being used to generate the frequency MM.INFO(PWM DUTY slice,channel) gives the counts at which the output transitions int wrap=(CPU_Speed*1000)/frequency; if(duty1>=0.0)high1=(int)((MMFLOAT)CPU_Speed/frequency*duty1*10.0); if(duty2>=0.0)high2=(int)((MMFLOAT)CPU_Speed/frequency*duty2*10.0); while(wrap>65535){ wrap>>=1; if(duty1>=0.0)high1>>=1; if(duty2>=0.0)high2>>=1; div<<=1; } if(div>256)error("Invalid frequency"); wrap--; if(high1)high1--; if(high2)high2--; Edited 2024-10-10 20:21 by matherp |
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| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
Hi Pete. But where you have 50% duty cycle = 31499, what if I want a smaller increment than 0.1%? If the granularity is 0.1% then surely my effective range is 1000 (<10-bit)? |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9104 |
What more do you want?  |
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| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
DOH! I guess I was taking the one decimal as an indicator:  I thought my motor was running kinda great Now I know why. |
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