Column: JESD204 standard


Testing with the JESD204B standard


By Frank Farrelly, Product Engineering Manager, Analog Devices, and Chris Loberg, Senior Technical Marketing Manager, Tektronix


Figure 1: Serial decode of a JESD204B data lane at 6Gbps showing the beginning of the ILAS


the specification and compile a list of functions to test. One category of protocol tests are test


A 14 November 2021 www.electronicsworld.co.uk


sequences. For PHY testing, JESD204B transmitters must be able to output scrambled jitter patterns (JSPAT) and modified random patterns (RPAT). From a protocol standpoint, there’s a need to validate that those patterns are correct. Te same is true with JESD204B receivers and the jitter tolerance scrambled pattern (JTSPAT). Optionally, if they support pseudorandom binary sequence (PRBS) patterns, those need to be validated too. Next are the short- and long-transport


layer patterns. These are included to help system developers debug their systems by proving the link is working correctly through the transport layer. From a component manufacturer standpoint, those transport-layer patterns have to be validated for every mode of operation the device supports, which, considering the number of link


s with the physical layer (PHY) tests, there is no official list of JESD204B protocol tests, so it’s left to each user to scour through


configuration variables, ends up being a lot of cases. One question that comes up regarding


protocol testing is how to do it at 12.5Gbps. One solution is to use a high- speed oscilloscope with a serial data decoder. Many higher-end oscilloscopes are now equipped with a dedicated trigger chip for triggering on 8B/10B data such as that used in JESD204B. Figure 1 shows serial decode of a JESD204B data lane at 6Gbps at the beginning of the initial lane alignment sequence (ILAS).


ILAS-based protocol testing Another group of protocol tests can be built around the ILAS. The ILAS as a whole is fairly complex, so breaking it down into its individual components can make protocol testing more meaningful. The following are some examples of tests that can be measured on a transmitter to validate its operation: Is the multi-frame length correct?


Does each multiframe start with an /R/ control code and end with an /A/ control code? Is the /Q/ control code in the right location? Is the link configuration data correct and in the right location? The ILAS contains data;


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