Electronic – the difference between a multiplexed bus and a multi-master bus

busetherneti2crs485serial-bus

The jargon of terms in bus architecture literature is half the difficulty in understanding it. At some places the term 'multiplexed' bus is used while at some other places 'multi-master' bus is used. They both look same to me but maybe they are different in some sense also. How to know what exactly is the meaning of these two terms?

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Muli-master is mainly for long serial communications. A bunch of masters on the same bus can simultaneously attempt to initate a transmission. Like a bunch of people trying to yell over each other in a room until everyone settles down to listen to just one person.

Multi-plexed is only (I think) for parallel processor to memory communications. It is definitely only for parallel since it has no meaning in serial. It is where not every line is dedicated to only a single address or data bit. Some lines might be used/shared for a low and high bit of the same type, or a data and address bit. This lets you reduce the number of lines between processor and memory at expense of speed.

These two things appear in different places. I don't know why they might ever overlap in application.

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Electronic – Multiplexing an I2C bus between two masters on a Xilinx FPGA

Just for the sake of completeness (since I was recently reminded about this question) I'll restate the answer that I finally settled on:

Given the following MPD snippet provided by the core vendor:

PORT IIC_DATA = "", DIR = IO, THREE_STATE=TRUE
PORT IIC_CLOCK = "", DIR = O, THREE_STATE=TRUE

I replace it with the following:

PORT IIC_DATA_I = "", DIR = I
PORT IIC_DATA_O = "", DIR = O
PORT IIC_DATA_T = "", DIR = O
PORT IIC_DATA = "", DIR = IO, THREE_STATE=TRUE, TRI_I = IIC_DATA_I, TRI_O = IIC_DATA_O, TRI_T = IIC_DATA_T
PORT IIC_CLOCK_O = "", DIR = O
PORT IIC_CLOCK_T = "", DIR = O
PORT IIC_CLOCK = "", DIR = O, THREE_STATE=TRUE, TRI_O = IIC_CLOCK_O, TRI_T = IIC_CLOCK_T

This works fine (as the underlying signals were defined in the VHDL anyway). It's a little bit of a hassle as I have to remember to do this each time I get an updated core from the vendor, but this is infrequent enough to not be a big deal. (I've been trying to persuade the vendor to add it themselves, but haven't had much luck thus far.)

Electronic – Difference between a bus and a wire

A wire can be a bus if it is a serial link carrying many individual pieces of information. More usually, a bus is regarded as a collection of wires that transport digital information from A to B. 64 bit processors (PCs etc.) have a 64 bit-wide bus between the CPU and their memory chips and possibly to other devices.

It doesn't have to be inside a computer of course - anything that is transmitting information from A to B will use some form of wire or collection of wires for achieving those aims.

What differentiates a wire as not being a bus is that it only carries one coherent "entity" such as power or a microphone signal or is connected to an on/off switch or a guitar or a speaker. A bus is usually digital.

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Electronic – Multiplexing an I2C bus between two masters on a Xilinx FPGA

Electronic – Difference between a bus and a wire

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