SNAS698C May 2020 – November 2022 LMK04832-SP
PRODUCTION DATA
The SYNC and SYSREF signals share the same SYNC/SYSREF Clock Distribution path. To properly use SYNC and/or SYSREF for JESD204B it is important to understand the SYNC/SYSREF system. Figure 8-2 illustrates the detailed diagram of a clock output block with SYNC circuitry included. Figure 8-3 illustrates the interconnects and highlights some important registers used in controlling the device for SYNC/SYSREF purposes.
To reset or synchronize a divider, the following conditions must be met:
Table 8-2 illustrates the some possible combinations of SYSREF_MUX and SYNC_MODE.
NAME | SYNC_MODE | SYSREF_MUX | OTHER | DESCRIPTION |
---|---|---|---|---|
SYNC Disabled | 0 | 0 | CLKin0_DEMUX ≠ 0 | No SYNC will occur. |
Pin or SPI SYNC | 1 | 0 | CLKin0_DEMUX ≠ 0 | Basic SYNC functionality, SYNC pin polarity is selected by SYNC_POL. To achieve SYNC through SPI, toggle the SYNC_POL bit. |
Differential input SYNC | X | 0 or 1 | CLKin0_DEMUX = 0 | Differential CLKin0 now operates as SYNC input. |
JESD204B Pulser on pin transition. | 2 | 2 | SYSREF_PULSE_CNT sets pulse count | Produce SYSREF_PULSE_CNT programmed number of pulses on pin transition. SYNC_POL can be used to cause SYNC through SPI. |
JESD204B Pulser on SPI programming. | 3 | 2 | SYSREF_PULSE_CNT sets pulse count | Programming SYSREF_PULSE_CNT register starts sending the number of pulses. |
Re-clocked SYNC | 1 | 1 | SYSREF operational, SYSREF Divider as required for training frame size. | Allows precise SYNC for n-bit frame training patterns for non-JESD converters such as LM97600. |
External SYSREF request | 0 | 2 | SYSREF_REQ_EN = 1 Pulser powered up | When SYNC pin is asserted, continuous SYSERF pulses occur. Turning on and off of the pulses is synchronized to prevent runt pulses from occurring on SYSREF. |
Continuous SYSREF | X | 3 | SYSREF_PD = 0 SYSREF_DDLY_PD = 0 SYSREF_PLSR_PD = 1 (1) | Continuous SYSREF signal. |
Re-clocked SYSREF distribution | 0 | 0 | SYSREF_DDLY_PD = 1 SYSREF_PLSR_PD = 1 SYSREF_PD = 1. | Fan-out of CLKin0 reclocked to the clock distribution path. |
Because the SYNC/SYSREF signal is reclocked by the Clock Distribution Path, an active clock must be present on the Clock Distribution Path (either from VCO or Fin0/Fin1 pins in distribution mode) for SYNC to take effect.
Any device clock divider or the SYSREF divider which does not have the SYNC_DISX bit or SYNC_DISSYSREF bit set will reset while SYNC/SYSREF Distribution Path is high. This is especially important for the SYSREF divider which has the ability to reset itself if the SYNC_DISSYSREF = 0! Be sure to set SYNC_DISX/SYNC_DISSYSREF bits as required.
While using Divide-by-2 or Divide-by-3 for DCLK_X_Y_DIV, SYNC procedure requires to first program Divide-by-4 and then back to Divide-by-2 or Divide-by-3 before doing SYNC.