SLAS669E September 2010 – may 2020 ADS5400-SP
PRODUCTION DATA.
Determining the closure of timing or validating the digital interface can be difficult in normal operation. Therefore, test patterns are available in register 0x06. One pattern toggles the outputs between all 1s and all 0s. Another pattern generates a 7-bit PRBS (pseudo-random bit sequence).
In dual bus mode, the toggle mode could be in the same phase on bus A and B (bus A and B outputting 1s or 0s together), or could be out of phase (bus A outputting 1s while bus B outputs 0s). The start phase cannot be controlled.
The PRBS output sequence is a standard 27-1 pseudo-random sequence generated by a feedback shift register where the two last bits of the shift register are exclusive-OR’ed and fed back to the first bit of the shift register. The standard notation for the polynomial is x7 + x6 + 1. The PRBS generator is not reset, so there is no initial position in the sequence. The pattern may start at any position in the repeating 127-bit long pattern and the pattern repeats as long as the PRBS mode is enabled. The data pattern from the PRBS generator is used for all of the LVDS parallel outputs, so when the pattern is ‘1’ then all of the LVDS outputs are outputting ‘1’ and when the pattern is ‘0’ then all of the LVDS drivers output ‘0’. To determine if the digital interface is operating properly with the PRBS sequence, the user must generate the same sequence in the receiving device, and do a shift-and-compare until a matching sequence is confirmed.