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Author Topic: 245 FIFO modes: Ok for WR to remain high between writes? (FT240X, FT245)  (Read 1333 times)

Jaholmes

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I'm building a USB sensor application using discrete logic--no MCU or CPU.  I have a few candidate designs drawn up, and noticed that I could simplify things if it was permissible to keep WR normally high, then pulse low-high to write.  Datasheets for the FT240X and FT245 are a bit ambiguous about this.  I should mention that I'm also reading bytes, so RD must also being pulsed low-high periodically.  Can this happen while WR is held high--without anything bad happening?  Or must WR be low to read?  I'd guess it would be ok, but figure I ought to put it out there just in case.

Very best,
Aaron
« Last Edit: December 02, 2019, 07:02:30 PM by Jaholmes »
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johnlon

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Re: 245 FIFO modes: Ok for WR to remain high between writes? (FT240X, FT245)
« Reply #1 on: January 19, 2021, 01:53:45 AM »

Using the UM245R module which carries the FT245.
I hold the read and write lines high by default and only bring RD low to get the necessary -ve edge to make the data available - it must return high for RXF to reset.
I bring write low to clock out the data but the return it high again after at least 50ns. 
Seems to work.
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