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From: "petrus bitbyter"
References: <email@example.com> <3DC41C51.2E0DF2FE@webaccess.net>
Subject: Re: Frustrated over converting 8 bit bcd to serial data
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Sun, 03 Nov 2002 19:22:55 GMT
NNTP-Posting-Date: Sun, 03 Nov 2002 20:22:55 MET
Organization: chello broadband
"Chuck Simmons" schreef in bericht
> Randy Ott wrote:
> > The Burr Brown part uses a three-wire SPI interface which requires more
> > a simple shift register.
> > "Gary Tait" wrote in message
> > news:firstname.lastname@example.org...
> > > >You need a parallel to serial shiftregister.
> > > >
> > >
> > > Such as a 4021. Just run it twice.
> In the case of the full SPI (4 wire), it really is almost as simple as a
> shift register since enable can double as a strobe. It becomes a bit
> gruesome when SDI and SDO are combined as one wire because the timing is
> not well defined and some manufacturers do not present data quickly
> enough for a single operation read. This is particularly true of some
> modern devices with 128 registers and more. To make matters even more
> interesting, there are several variants that use opposite polarity
> enable, use inverted data or use the other clock edge to indicate data
> valid. Other variants of SPI use configurable bit streams that can be of
> any length (even Motorola has done this and Atmel has two chips in the
> same family that use different polarity read/write bits). However, to
> write to a peripheral only, the interface is quite simple. The SPI
> horrors created by SSI and others are mainly problematic for reading
> data from the peripheral.
> BTW, one way around the readback problems on 3 wire SPI is to use a very
> slow clock. This allows plenty of time for the data to ripple through
> deeply nested multiplexers and load in the peripheral output shift
> register. I have this working well with both SSI and Atmel parts.
> ... The times have been,
> That, when the brains were out,
> the man would die. ... Macbeth
> Chuck Simmons email@example.com
The datasheet is on the Texas website and tells all you need to know.
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