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LMX1204EVM: SYSREF Pulsed mode functional issue

George Lucian Chiriac
Prodigy 40 points
Part Number: LMX1204EVM
Other Parts Discussed in Thread: LMX1204

Hi Team,

I'm using the LMX1204EVM in order to evaluate the possibility to integrate the LMX1204 on a custom PCB board.

The purpose is to use the SYSREF in pulsed mode, issuing a request of pulses through SPI. I've followed the specification in the Datasheet and in the EVM Application note, and with SYSREF continuous i haven't any problems.

When i configure the SYSREF in pulsed mode, i expect a certain mode of operation, like issuing a SPI request (toogling the sysref request bit from 0 to 1, R72 (0x48) bit 2, i expect to see the number of pulses desired, but that not happens. When i set the bit to 0, the SYSREF output continuosly generate repeated pulses, when i set to 1, the SYSREF outputs go all to 0.

I figure out that, the expected result is obtained in the following way:

  • Set SYSREF_MODE = SYNC -> @write R14(0x0E) 0x0000 
  • Set SYSREFREQ_SPI = LOW -> @write R72(0x48) 0x0000 
  • Set SYSREFREQ_SPI = HIGH -> @write R72(0x48) 0x0004
  • Set SYSREF_MODE = SYSREF -> @write R14(0x0E) 0x0002 

In this way, the output is the desired one like 8 pulses and after that the output is 0. Is supposed to work like that? I didn't expect this. I expect that the SYSREF_MODE remains set to SYSREF and only when i issue a LOW-HIGH transition on SYSREFREQ_SPI field the device outputs the desired number of pulses. I attach also the configuration file that i use in the TICS PRO.

Can someone helping me to issue that?

Thanks!

Best regards.


conf1+sysref_pulsed.tcs 

conf1_sysref_pulsed.txt 
R90	0x5A0000
R86	0x560004
R79	0x4F0005
R75	0x4B0003
R72	0x480000
R67	0x4351CB
R65	0x4165F0
R34	0x2204C0
R33	0x210000
R29	0x1D05FF
R28	0x1C0A08
R25	0x190119
R24	0x180001
R23	0x17E040
R22	0x16046C
R21	0x15276C
R20	0x14276C
R19	0x13276C
R18	0x12276C
R17	0x110139
R16	0x108200
R15	0x0F0B80
R14	0x0E0000
R13	0x0D0001
R12	0x0C0000
R11	0x0B0000
R9	0x09C004
R8	0x080130
R7	0x070001
R6	0x06C924
R5	0x05493F
R4	0x043FFF
R3	0x033F87
R2	0x020083
R0	0x000000

  • +1
    TI__Genius 12560 points

    Hi,

    The configuration file looks good. To operate the SYSREFREQ in SPI mode (as SYNC through SPI or SYSREF pulse generation), the SYSREFREQ pins should be at logic low state, then only the SPI control bit works. This is missing in current datasheet and will be updating in latest update.

    To keep the SYSREFREQ pin on logic low, you can follow the below circuit, which would provide the _N pin higher level than _P and it would accept the SYSREFREQ_SPI bit.

    The used sequence by you is not the correct, which is just send the pulses as soon as changing the SYSREFREQ_MODE  status from SYNC to SYSREF.

    Thanks!

    Regards,
    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Prodigy 40 points

    Hi Ajeet, thank you for your reply.

    That sounds good. I will try as soon as possible to implement the configuration setup that you suggest me.

    Ajeet Pal said:
    The used sequence by you is not the correct, which is just send the pulses as soon as changing the SYSREFREQ_MODE  status from SYNC to SYSREF.

    I also suppose that, this is why i ask your confirmation.

    I will you know that this configuration figure out my problem. 

    Thanks! 

    Best Regards.