DS90UB926Q-Q1 Datasheet, PDF (24/57 Pages) Texas Instruments – 5- to 85-MHz 24-Bit Color FPD-Link III Deserializer With Bidirectional Control Channel

DS90UB926Q-Q1
SNLS422B – JULY 2012 – REVISED JANUARY 2015
NOTE
BIST is not available in backward-compatible mode.
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7.3.17.1 BIST Configuration and Status
The BIST mode is enabled at the deserializer by the Pin select (Pin 44 BISTEN and Pin 16 BISTC) or
configuration register (Table 11) through the deserializer. When LFMODE = 0, the pin based configuration
defaults to external PCLK or 33 MHz internal Oscillator clock (OSC) frequency. In the absence of PCLK, the user
can select the desired OSC frequency (default 33 MHz or 25MHz) through the register bit. When LFMODE = 1,
the pin based configuration defaults to external PCLK or 12.5MHz MHz internal Oscillator clock (OSC) frequency.
When BISTEN of the deserializer is high, the BIST mode enable information is sent to the serializer through the
Back Channel. The serializer outputs a test pattern and drives the link at speed. The deserializer detects the test
pattern and monitors it for errors. The PASS output pin toggles to flag any payloads that are received with 1 to
35 bit errors.
The BIST status is monitored real time on PASS pin. The result of the test is held on the PASS output until reset
(new BIST test or Power Down). A high on PASS indicates NO ERRORS were detected. A Low on PASS
indicates one or more errors were detected. The duration of the test is controlled by the pulse width applied to
the deserializer BISTEN pin. This BIST feature also contains a Link Error Count and a Lock Status. If the
connection of the serial link is broken, then the link error count is shown in the register. When the PLL of the
deserializer is locked or unlocked, the lock status can be read in the register. See Table 11.
7.3.17.1.1 Sample BIST Sequence
See Figure 17 for the BIST mode flow diagram.
1. For the DS90UB925Q-Q1 and DS90UB926Q-Q1 FPD-Link III chipset, BIST Mode is enabled through the
BISTEN pin of DS90UB926Q-Q1 FPD-Link III deserializer. The desired clock source is selected through
BISTC pin.
2. The DS90UB925Q-Q1 serializer is woken up through the back channel if it is not already on. The all zero
pattern on the data pins is sent through the FPD-Link III to the deserializer. Once the serializer and the
deserializer are in BIST mode and the deserializer acquires Lock, the PASS pin of the deserializer goes high
and BIST starts checking the data stream. If an error in the payload (1 to 35) is detected, the PASS pin will
switch low for one half of the clock period. During the BIST test, the PASS output can be monitored and
counted to determine the payload error rate.
3. To Stop the BIST mode, the deserializer BISTEN pin is set Low. The deserializer stops checking the data.
The final test result is held on the PASS pin. If the test ran error free, the PASS output will be High. If there
was one or more errors detected, the PASS output will be Low. The PASS output state is held until a new
BIST is run, the device is RESET, or Powered Down. The BIST duration is user controlled by the duration of
the BISTEN signal.
4. The Link returns to normal operation after the deserializer BISTEN pin is low. Figure 18 shows the waveform
diagram of a typical BIST test for two cases. Case 1 is error free, and Case 2 shows one with multiple errors.
In most cases it is difficult to generate errors due to the robustness of the link (differential data transmission
etc.), thus they may be introduced by greatly extending the cable length, faulting the interconnect, reducing
signal condition enhancements ( Rx Equalization).
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