MESA PWM

kostas
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13 Feb 2014 23:05 #43828 by kostas

Replied by kostas on topic MESA PWM

PCW wrote:
That said, Its probably possible to make a bitfile with inverted PWM output with some minor VHDL hacking

How?

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PCW
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13 Feb 2014 23:19 - 13 Feb 2014 23:20 #43830 by PCW

Replied by PCW on topic MESA PWM

As a quit hack, changing:

	if (UNSIGNED(maskedrefcount) < UNSIGNED(pwmval)) then 
		pwm <= '1'; 
	else 
		pwm <= '0';
	end if;

to

	if (UNSIGNED(maskedrefcount) < UNSIGNED(pwmval)) then 
		pwm <= '0'; 
	else 
		pwm <= '1';
	end if;

in pwmpdmgen.vhd should work

Last edit: 13 Feb 2014 23:20 by PCW. Reason: formatting

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eslavko
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14 Feb 2014 02:44 #43834 by eslavko

Replied by eslavko on topic MESA PWM

Use hardware watchdog!!!
At startup ALL driver enable should be dissabled. When LinuxCNC starts then use F1 estop latch to kick watchdog on hardware pin. So in meantime you should set other pins correctly. Kep this as safery feature. When you plug in machine nothing should happen! Even when PC is booted up. (if you use just parport then there is mess of signals in bootup process) NOTHING SHOULD HAPPEN UNTIL YOU PRES F1 AND/OR EXTERNAL POWERON BUTTON.

This cost one extra releay and few diodes to make chargepump. It cost nothing compared to fingers!

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kostas
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14 Feb 2014 03:54 #43835 by kostas

Replied by kostas on topic MESA PWM

This works as advertised. Thanks Peter!

Eslavko, that's why I'm worried of this small pulse at the beggining.
I probably should have an enable pin in my hardware somewhere but for the work I'm doing now it does not really matter and there are no safety issues.
This is a very small machine, actually a toy of mine. Anyway, this should work ok now.

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eslavko
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14 Feb 2014 04:24 #43836 by eslavko

Replied by eslavko on topic MESA PWM

kostas wrote:
This is a very small machine, actually a toy of mine. Anyway, this should work ok now.

Even toy machine can drill trought a finger...
At least wire E-Stop properly. Don't rely on F1/ESC. The LinuxCnc window can lost focus and keyboard will not respond.

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vre
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20 Jul 2014 06:29 #48957 by vre

Replied by vre on topic MESA PWM

What is max pwm frequency for driving spindle with mesa cards ?
Also can i change that frequency to 5khz or 10khz ?

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PCW
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20 Jul 2014 09:14 #48960 by PCW

Replied by PCW on topic MESA PWM

The PWM rate is settable to a few Hz up to ClockHigh/512
Clock high is either 100 MHz or 200 Mhz depending on FPGA card

This makes the maximum PWMrate ~192 KHz or ~384 KHz depending on FPGA card

The PWM rate is a global setting however so if you have multiple devices using the PWM,
they all have to use the same frequency. The PDM rate setting is separate however so if you
need different rates, and some devices can use PDM (7I48 and 7I33 can for example) this allows
an independent PWM rate to be set

The following user(s) said Thank You: vre

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vre
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20 Jul 2014 11:32 #48961 by vre

Replied by vre on topic MESA PWM

I have only one device that takes input up to 10khz so that covers me completely.

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