JESD204C Intel® Stratix® 10 FPGA IP Design Example User Guide

ID 683357
Date 11/22/2021
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3.1.4. SYSREF Generator

SYSREF is a critical timing signal for data converters with JESD204C interface.

The SYSREF generator in the design example is used for the duplex JESD204C IP link initialization demonstration purpose only. In the JESD204C subclass 1 system level application,you must generate SYSREF from the same source as the device clock.

For the JESD204C IP, the SYSREF multiplier (SYSREF_MULP) of the SYSREF control register defines the SYSREF period, which is n-integer multiple of the E parameter.

You must ensure E*SYSREF_MULP ≤16. For example, if E=1, the legal setting for SYSREF_MULP must be within 1–16, and if E=3, the legal setting for SYSREF_MULP must be within 1–5.

Note: If you set an out-of-range SYSREF_MULP, the SYSREF generator will fix the setting to SYSREF_MULP=1.

You can select whether you want the SYSREF type to be a one-shot pulse, periodic, or gapped periodic through the Example Design tab in the JESD204C Intel® FPGA IP parameter editor.

Table 10.  Examples of Periodic and Gapped Periodic SYSREF Counter
E SYSREF_MULP SYSREF PERIOD

(E*SYSREF_MULP*16)

Programmable Duty Cycle Description
1 1 16 1..15 Gapped Periodic
1 1 16 Auto (8) Periodic
1 2 32 1..31 Gapped Periodic
1 2 32 16 Periodic
1 3 48 1..47 Gapped Periodic
1 3 48 Auto (24) Periodic
1 16 256 1..255 Gapped Periodic
1 16 256 Auto (128) Periodic
2 1 32 1..31 Gapped Periodic
2 1 32 16 Periodic
2 2 64 1..31 Gapped Periodic
2 2 64 Auto (32) Periodic
2 3 96 1..95 Gapped Periodic
2 3 96 Auto (48) Periodic
2 8 256 1..255

Gapped Periodic

E*SYSREF_MULP <=16

2 8

(Illegal<9..16>)

256 Auto (128) Periodic
Note: If you assign an illegal SYSREF_MULP value, the the SYSREF period defaults to 32.
16 1

Illegal<2..16>

256 1..255

Gapped Periodic

E*SYSREF_MULP <=16

Table 11.  SYSREF Control RegistersYou can dynamically reconfigure the SYSREF control registers if the register setting is different than the setting you specified when you generated the design example. Configure the SYSREF registers before the JESD204C Intel® FPGA IP is out of reset. If you select the external SYSREF generator through the sysref_ctrl[7] register bit, you can ignore the settings for SYSREF type, multiplier, duty cycle and phase.
Bits Default Value Description
sysref_ctrl[1:0]
  • 2‘b00: One-shot
  • 2‘b01: Periodic
  • 2'b10: Gapped periodic

SYSREF type.

The default value depends on the SYSREF mode setting in the Example Design tab in the JESD204C Intel® FPGA IP parameter editor.

sysref_ctrl[6:2] 5'b00000

SYSREF multiplier.

This SYSREF_MULP field is applicable to periodic and gapped-periodic SYSREF type.

You must configure the multiplier value to ensure the E*SYSREF_MULP value is between 1 to 16 before the JESD204C IP is out of reset. If the E*SYSREF_MULP value is out of this range, the multiplier value defaults to 5'b00001.

For example:

If E =1, write 5'b10000 to sysref_ctrl[6:2] to set the SYSREF_MULP decimal value of 16.

sysref_ctrl[7]
  • Duplex datapath: 1'b1
  • Simplex TX or RX datapath: 1'b0

SYSREF select.

The default value depends on the SYSREF mode setting in the Example Design tab in the JESD204C Intel® FPGA IP parameter editor.

  • 0: External SYSREF
  • 1: Internal SYSREF
sysref_ctrl[15:8] 8'h00

SYSREF duty cycle when SYSREF type is periodic or gapped periodic.

You must configure the duty cycle before the JESD204C IP is out of reset.

Maximum value = (E*SYSREF_MULP*16)-1

For example:

50% duty cycle = (E*SYSREF_MULP*16)/2

If you do not configure this register field, the duty cycle defaults to 50%.

sysref_ctrl[16] 1'b0

SYSREF phase (for sysref_out output port).

  • 0: Positive edge
  • 1: Negative edge
sysref_ctrl[17] 1'b0

Manual control when SYSREF type is one-shot.

  • Write 1 to set the SYSREF signal to high.
  • Write 0 to set the SYSREF signal to low.

You need to write a 1 then a 0 to create a SYSREF pulse in one-shot mode.

sysref_ctrl[31:18] Don't Care Reserved.

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