LMK04828: SYSREF - continuous mode

Sowri Rekha Devanaboyina

Part Number: LMK04828
Other Parts Discussed in Thread: LMK04828, TICSPRO-SW

Hi,

I've couple of questions regarding LMK04828 SYSREF generation.

1) I'm trying to generate continuous mode of SYSREF signal using LMK04828. When I probe my SYSREF signal, it always stays at logic HIGH (1.0V).

VCO frequency = 3000 MHz

SYSREF Clock Divider = 300

So I can generate SYSREF at 10 MHz continuously. I've configured my registers accordingly. Please check my register settings in the attached MAC file (codeloader4 settings). If you could provide me sample code or register flow to generate SYSREF - continuous mode, that would be really helpful.

2) After the registers are programmed from 0x000 to 0x1FFF, I'm not able to perform write event to any register.

For instance: if I want to write into Reg 0x143 once the programming sequence is done (0x000 - 0x1FFF), I am not able to perform write event. However I can read the old value back. Is it expected behavior?

Registers 0x1FFD - 0x1FFF are programmed to default values meaning that "Registers unlocked".

Please help me with the above inquiries.

Thanks,

Rekha

over 8 years ago

0 Timothy T over 8 years ago

TI__Mastermind 28590 points

Hello,

I didn't see your attachment of registers. However, please download the ticspro-sw, I think you will find configuring the SYSREF and device in general to be much better using this software.

73,
Timothy

0 Sowri Rekha Devanaboyina over 8 years ago in reply to Timothy T

Prodigy 70 points

Hi Timothy,

Thank you for suggesting TICS Pro software. I can now successfully generate SYSREF signal. Can you please provide me the procedure to calculate SYSREF frequency. I'm using the below configuration:

Data Rate = 10Gbps

Device Clock = 250 MHz

Number of Frames per multi frame (K) = 32

Local Multiframe Clock (LMFC) = Device clock / (4 * K) = 250 / (4*32) = 1.95 MHz

SYSREF Frequency = LMFC / (2^n) = 1.95 / 2 = 0.976 MHz

Please let me know.

Thanks,

Rekha

0 Timothy T over 8 years ago in reply to Sowri Rekha Devanaboyina

TI__Mastermind 28590 points

If your SYSREF frequency is 0.975 MHz (0.976 is a type above), a CLKout 250 MHz, then you would need a VCO with a frequency of at least LCM(0.975 MHz, 250 MHz) = 9.75 GHz. So unfortunately this combination would not work as our VCO frequency does not reach this.

Can you adjust the numbers?

73,
Timothy

0 Sowri Rekha Devanaboyina over 8 years ago in reply to Timothy T

Prodigy 70 points

Hello Timoothy,
Thank you for the clarification. I got generalized expression to calculate SYSREF values from the below website: www.ti.com/.../sbaa221.pdf
SYSREF = fS/ LCM(64,20 × K) / N where N is a integer (1,2…) , fS is Sampling Clock

Using this formula, I'm not able to achieve the range that you mentioned in the previous response. Please let me know if I miss anything here.

Thank you in advance.
Regards,
Rekha

0 Timothy T over 8 years ago in reply to Sowri Rekha Devanaboyina

TI__Mastermind 28590 points

Let me check with some of the ADC folks on this..

0 Timothy T over 8 years ago in reply to Timothy T

TI__Mastermind 28590 points

Can you advise the ADC you are using and what data format you are planning to use?

73,
Timothy

0 Sowri Rekha Devanaboyina over 8 years ago in reply to Timothy T

Prodigy 70 points

I'm using AD9234 and currently testing PRBS 7 pattern with line rate 10Gbps.

Thanks,

Rekha

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LMK04828: SYSREF - continuous mode