SPI and Microwire
Peter L. Peres email (remove spam text)
On Sat, 28 Nov 1998, Morgan Olsson wrote:
> I thougt it was the same (shift register technique)
Microwire is (C) [pat] [tm] Motorola, whereas SPI is an acronym that
cannot be patented...
> Now i see that Mchip have different SPI and Microwire EEPROMS
> And also there seem to be different modes in SPI
Not just Microchip but many others have different modes of SPI (including
> What is the difference?
There are three kinds of major differences: edge/level signalling,
positive/negative logic, and addressing.
The edge/level problem applies to ~SS especially, i.e. sometimes it is ok
to pulse ~SS after sending the required no. of clocks, or it has to be H
or L during all this time. There are also parts that clock in on the
high-going edge etc.
The addressing refers to the fact that some SPI part manufacturers choose
to address distinct functions in a chip by the number of clock pulses
until ~SS is (un)asserted. Motorola is one of these BTW.
> Does anyone know where to get the specs?
The Microwire specs are available on Motorola's site, I think as a part of
some HC11 (?) processor's data sheet. They will not do you a lot of good
if you work with other manufacturer's parts.
A reasonably flexible SPI library needs:
- Programmable ~SS and SCK polarity
- ~SS programmable as strobe pulse or enable
- Capacity to send or receive 1-N bits of data (yes, in increments of 1)
hope this helps,
In reply to: <firstname.lastname@example.org>
See also: www.piclist.com/techref/io/serial/spis.htm?key=spi
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