Question regarding SPI (Serial Peripheral Interface)

These are not official names, they're just what the manufacturers call them. "SPI" is pretty common terminology, but one manufacturer's SPI port won't necessarily be exactly the same as another's, nor will their terminology necessarily be the same.

The short story is: look at the data sheets.

The "SPI" is the trade mark of Motorola as well as the term "I2C" is proprietary to Philips (or whatever those companies are called now). For that reason the others have to use nicknames.

Datasheets are boring. Let's talk about something else.

VLV

From this link:

When I look at the lines:

a.. SCLK - Serial Clock (output from master) a.. MOSI - Master Output, Slave Input (output from master)

SCLK and MOSI can be the inverse of each other. Thus if one were to look at this datasheet:

I am thinking Clock+ and Clock- are the same as SCLK and MOSI in SPI.

Can anyone tell me if this is a correct assumption?

Thanks.

No, the device has two differential clock lines, clock+ and clock-, and two differential data lines, data+ and data-. These are RS-485/ RS-422 signals. You'll need to have a suitable driver and receiver at your end to convert them to the single-ended signals you'll feed into your micro. From the datasheets you provided it appears that they also have TTL-level products if you're sure you don't need the differential signals and if you have the luxury of picking the parts.

It is an incorrect assumption. It should be:

SCLK connect to Clock+ and Clock- (via MAX488 or similar) MOSI not connected MISO connect to Data+ and Data- (via MAX488 or similar)

If this is a hardware SPI port then you should know that usually the only way to drive SCLK is to output a byte (or several bytes) of data to MOSI. In this case it doesn't matter what is sent to MOSI since it is not connected to anything.

Please don't use the SCLK/MOSI combination to get around buying a cheap differential driver. SCLK and MOSI will most probably be out of phase and may or may not damage your hardware at the other end.

SPI is clocked data clock, Data out, data in, chip select. Then there are the variations. Like combining data in and data out. The hard stuff comes with the "data sheet stuff" Data clocks on rising edge, data clocks on falling edge Data valid High, Data Valid low.

If your question was really can I connect a SSI encoder to the SPI port on my microcontroller, the answer is Yes! I have done this on a Freescale HC08's SPI port simply by passing the MISO and SCLK through a DS8921.

Regards David

Can anyone recommend a multiplexer (or whatever you call it) that can be used to connect multiple SSI encoders to a single SPI input? I figured I can send the same Clock+ and Clock- via the same differential driver to all the encoders. And then use the MOSI (or some other I/O line) to talk this multiplexer to get each encoder's data.