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Multiplexing for an LED display?
**broken link removed**
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...
aaawe! google for it! https://en.wikipedia.org/wiki/Multiplexing
Could also be like a multiplexed bus where "address" and "data" flow along the same wires but at different times.
dknguyen said: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).
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.
No, lets say you have some SRAM instead. Way easier to explain with going into refresh cicuitry etc....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.
No, lets say you have some SRAM instead. Way easier to explain with going into refresh circuitry 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
Marks256 said:Thanks AllanBertelsen, but i am just getting lost more and more. I get how to hook up the RAM, but i don't get the other things. What do you mean "You can only address one bit at a time"? Do you mean that the RAM is serial, instead of parallel? I am SO lost! Please don't give up on me yet!
I don't understand why i need 1 data line to each of the RAMs? Here is a list of things i don't get;
1. How does the initial command get set in the CPU? (from the ROM to the CPU), there is no commands in the cpu to do this, so what happens? I think it is called bootstrap?
2. If all the address lines are used on the RAM, then how do you get more devices on the CPU?
These are all the questions i can think up right now. I am going to apply power to the CPU, and see what happens. I will put a few LED's on the address lines, and then see what they display. PLEASE HELP! I just can't completely visualize the "Big picture".