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chris_notsch's avatar
chris_notsch
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5 years ago

Forcibly specify correct toggle rate for LVDS pin

Dear Community, We are facing a critical issue in implementing a design using a Cyclone 10 LP with a pwm generator logic driving a LVDS pin. The resolution of the output logic is 1ns (1 Ghz delay...
JonWay_altera's avatar
JonWay_altera
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5 years ago

Hi @chris_notsch

Thanks for the design. I have a better idea now. You are trying to make a GPIO IO standard LVDS to toggle at 1GHz. It will message: Error (176060): The transmitter driving I/O pin pin_arduinobus_j7_4 at data rate 1000 Mbps exceeds the maximum allowed data rate of 740 Mbps for LVDS output

This is expected as the datasheet stated:

chris_notsch's avatar
chris_notsch
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5 years ago

@JonWay_C_Intel i was providing an example of the issue as you had requested in the simplest form possible. It was intended to show the error encountered, not the real application as this is a public forum and i cannot disclose the companys intellectual property in this manner.

To clarify: this error persists, independent of the toggle rate of the pin, as it is an issue with the quartus software deriving the real toggle rate and has nothing to do with the datasheet specification. To highlight this i have modified the example to a division factor of 4, now delivering instead of 500Mhz (=1Gbps) as before an output rate of 250MHz (=500Mbps) which is well within the datasheet specification. You can modify this to any arbitrary division factor, the issue will persist no matter how low you make the toggle rate of the pin:

I have attached the modified examples:
1) version failing during the fitting process "correct implementation of the PLL parameters"
2) successfully compilable "dynamic pll workaround"

These represent the equivalent counterparts to the previous examples:
1) "Config_TestProgram - Not working (1GHz PLL intitial)" (08-28-2020 01:06 PM)
2) "Config_TestProgram - Working (500MHz PLL initial)" (08-28-2020 01:06 PM)

If you wish to have a look to the actual application causing this problem, please provide me a means to contact you in a non-public fashion to exchange the data and / or arrange the potential shipment of the demonstation hardware.

Thank you,

-Chris