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75 lines
2.6 KiB
Plaintext
75 lines
2.6 KiB
Plaintext
= SPI Mux MCN rev2-E1
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== Rationale
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A couple of incorrect voltages were identified though testing of the spimux.
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. U2 pin10 (enable) should be a 3V3 signal rather than a 1V8 signal
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. U3 pins 14 and 24 (mux select) should be a 1V8 signal rather than a 3V3 signal.
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Note the rework documented here will use the spare channel on the level translator so that the flash mux select goes through the level translator from the SP.
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To fix the first issue, we're going to disconnect R2 from 1V8 and connect to 3V3 so SP_TRANS_EN is pulled up to 3V3.
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To fix the second issue, we're going to run the SP signal `SP_QSPI_XTRA10` through the level translator and also disconnect
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J5 pin 1 from 3V3 and connect it to 1V8.
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Additionally R4 and R5 are too weak to properly drive the bus (with the level translator) when nothing is connected. these will be changed to 3.3k Ohms.
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== Material/Tools
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Aside from normal lab tools like optical magnification, solder, flux, and tweezers, you'll need:
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. some 30ga wire,
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. qty 2 3.3k 0402 resistors (per board)
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. exacto knife for scraping/cutting traces.
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== Physical Rework steps
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To disconnect J5 pin1 from 3V3 and connect it to 1V8 do the following:
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. Cut the trace (`3V3`) between the silkscreen of `R2` and `R3`
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image::jumper_topside.png[Trace Cut]
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. Connect the now-disconnected size of R2 to 3V3 with a jumper wire as shown below in the 2nd picture.
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image::topside_jumper2.png[Jumper]
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. Cut the trace running along the top-side of the board `SP_QSPI_XTRA10` where indicated in red. (first picture)
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. Carefully expose the copper of the traces on either side of the cut to allow jumper wires to be soldered to these spots. (Light grey blocks in first picture below)
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. Solder a jumper (blue in first picture below) between the exposed trace and pin 12 of U2 (un-used Y8 of level translator)
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. Solder a jumper (orange in first picture below) between U2 pin 9 (un-used A8 of level translator) and the remaining exposed trace
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image::enable_level_trans.png[Level Trans]
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. Replace R4 and R5 on the top side of the board with 3.3k resistors.
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image::R4R5_replace.png[Pull-ups]
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. On the back side of the board, solder a jumper between J1 pin1 (`1V8`) and J5 pin 1 (see 2nd picture below)
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. On the back side of the board, the the trace (`1V8`) between J2 pin1 and the via, or optionally
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carfully drill the the via to disconnect from 1V8
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image::bottom-side_jumper.png[Bottom Side]
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Update the board marking:
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- Re-label board as rev2-E1
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Final example rework pictures:
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image::top_finished.jpg[Finished Top]
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image::bottom_finished.jpg[Finished Bottom]
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== Determinations
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Until spi-mux bring-up is complete no cad changes have been initiated.
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