On Tue, Mar 09, 1999 at 11:04:49PM +0800, C.H.Ling wrote:
> > Indeed. The widely used Serial Peripheral Interface only needs 3 wires
> > (data, clock, and ground), and Dallas Semiconductor makes a line of flash
> > ROMS that look a lot like overgrown silver-oxide batteries.
> Sorry, I think the serial interface's 3 wires are In, Out, Gnd.
Not the Serial Peripheral Interface as implemented by Atmel, Motorola, and
others...it's a bidirectional clocked bus with a master and a slave. (You
can implement multiple slaves with additional select lines, but that's not
needed for two devices.) It works because the slave never transmits without
an explicit grant from the master. The clock line is necessary to avoid any
timing dependencies, and simplify the circuitry required in the slave
device.
I dunno if the interface from the OM-77's lens to the camera is implemented
with SPI, or another interface, but it doesn't take a lot of hardware either
way.
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