Just as the title asks; what is multiplexing? I have the slightest idea, but i don't understand. Thanks.

 

Multiplexing for an LED display?

http://www.myplace.nu/avr/countermeasures/cm_sch.gif

The way it works is, there is a common connection for each segment in the display, each segment in 1 digit is referred to as a,b,c,d,e,f,g and dp for the decimal. (driven by pins D0-D7 in the schematic).

There is an enable signal (at the top of the LED displays) for each digit. By enabling each digit one at a time, and changing the 'D' pins at the same time, you can display a different number on each display. So if you wanted to display 123456 on the display, you would enable LED1 and set the 'D' pins to display a 1, then disable LED1 and enable LED2 and set the D pins to display a 2.

So each digit is only turned on for 1/6th of the time. By switching between the LEDs fast enough you cant even tell that they are being turned on and off. (about 20-30 times a second for the human eye). Also, the LEDs should be driven with alittle more current than the normal rating, since they will only be turned on 1/6th of the time, they will be dimmer than normal.

Hope this helps...

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Jeff
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

aaawe! google for it! http://en.wikipedia.org/wiki/Multiplexing

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i² = j² = k² = ijk = -1

 

in general sense, it is making use an object for multiple tasks...

1. Multiplexing a 7 segment display.
2. Multiplexing od the Data bus for address in 8085
3. multiplexing the T1 line for 24 telephone channels.

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Bharath Bhushan Lohray.
M.Sc. Electronics.

 

Multiplexing is a circuit that lets you use one input pin and lets you switch it between the outputs of several devices. So you can use one pin on a uC to monitor several different things one at a time.

THat circuit, however, can be used for other more novel things because of the way it works (like truth tables and stuff).

 

Could also be like a multiplexed bus where "address" and "data" flow along the same wires but at different times.

 

My definition:

Passing many signals along one communication channel, all at the same time, or, one after the other.

Multiplexing takes many forms depending on where and how it is implemented.

JimB

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No, i meant for CPU's and RAM and what not. It did, however, explain to me how i have to use my multiplexing LED display! Thanks! Now i can finally use the bugger.


I did search google. All it told me was the fact that it takes multiple lines of data, and then transmits it over one line. No explanation, no help at all. So i asked here. But there was a link at the bottom that helped a little, so thanks anyways.


Yes, this is what i am referring to, with the addition of CPUs. So, if a CPU has one pin designated for two functions, then does it already have a built in multiplexer? Then how does it use them? Like on the 8088 processor, how does it know when to use the one or the other pin function? Or do they switch between them every clock cycle? I am so confused.
If the MUX outputs one of the data lines, how does the destination of the data know what bit of data it is receiving?

 

You can use most multiplexer ICs backwards as well. So, rather than one input pin being switched between several devices, you can have the outputs of several devices switched to one output pin. To use a multiplexer IC you normally have an address bus which selects which pin will be connected to the common line. So, for example, if you had a 3-bit Multiplexer IC you could switch the common line between 8 possible outputs (or inputs depending on which way around you use it). To select any of the 8 possible outputs you simply put a binary number on the chip's address bus which corresponds to the pin number you want to select.

Brian

 

Ok, now this brings me to another question. How does addressing work? I know it is sort of like using a mailing address to someones home, but how is the address assigned to certain chip? It is built in? Like, let's say that i have some DRAM, and a few other IC's that have address buses, how do i assign the addresses to the chips? I have about 30 DIP style DRAM chips, that i am just itching to use, but i don't quite know how to address yet.

 

Find the datasheets for the chips. Use http://www.datasheetcatalog.com for example. The data sheets are usually very specific about these matters. There can be differences from chip to chip, and you will only find these differences by reading the datasheets.

 

I have already got the datasheets for them. I was wondering if someone could leave a quick briefe/generic description on how this works?

 

No, lets say you have some SRAM instead. Way easier to explain with going into refresh cicuitry etc....
So, you have 8 (Not 30 to keep it simple) SRAM chips. You would parallel the address and data lines on all 8 chips and connect them to the CPU. Lets say the CPU has a 16bit address bus but your SRAM chips only have 13 address lines. You would take a 74HC138 demultiplexer and feed the unused CPU upper address lines into it. The 8 outputs would select each SRAM chips "chip enable line" so that only one SRAM would be accessed for each 0x1FFF block of memory from 0x0000 to 0xFFFF.
SRAM1 = 0x0000 - 0x1FFF
SRAM2 = 0x2000 - 0x3FFF
SRAM3 = 0x4000 - 0x5FFF
.
..
...
SRAM8= 0xE000 - 0xFFFF

 

Ok, i know this is a lot to ask of you, kchriste, but i was wondering if you would draw a diagram of that. I can see what you are talking about, but i cant quit visualise it. I have a Z80 CPU, i have the pinouts attached. I can visualise the RAM setup, but not with the multiplexer. Also, what if there were more things connected to the address bus? Such as I/O things. Would i use a multiplexer? I think this is starting to make sense! Could you please give me a little more information(and maybe a few diagrams)?

Also, i thought that DRAM had a built in refreshing circuits? Here is the part number for the DRAM i have; KM4164B.

Attached Images

z80.PNG (25.0 KB, 27 views)

 

You can only address one bit at a time with KM4164B. So If you stack 8 of these then the address pins are all connected (A0 from Z80 to A0 on every KM4164B) and one data pin from Z80 goes to each of the KM4164B.

Look at
http://www.sxlist.com/techref/mem/dram/slide1.html

A diagram for an 8bit dram as HM6116 can be seen here:
http://www.jdm.homepage.dk/z80cpu.gif