Name: Build an 8-bit decimal display for our 8-bit computer
Uploaded: 2020-03-27T16:57:15.000Z
Duration: 32 min 47 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Past simple

So in a previous video we used an eeprom as a decoder for a seven segment display

so by hooking up a binary input here, so this is [6] or you know 4

Gerund

5 by inputting a different binary number on the address lines of the eeprom the eeprom would output

Ones and zeros in the appropriate places to turn on or off the appropriate segment on the seven segment display

But how can we build a decoder for [8] bits that outputs a number from 0 to 255?

on three of these seven segment displays and

That question came up in the comments on the video about using an e eeprom as a 7 segment decoder

the YouTube Cuber asked what do I do if I have multiple seven segment displays is flying one decimal number and

So rest little teapot says if I've got this correctly you would need one e eeprom for each seven segment display

And that's exactly what what we've got here? We've got one e eeprom for each of the seven segment displays

So we've got a one place a eeprom for the one stage at a tens place

Then the address lines or at least the first eight of the address lines for the chips are all linked together

So if we put an address value on these eight lines here in this case

I'm putting that binary equivalent of 123 that same value is going to show up on each of these chips

So this chip is going to be at address 123

This chip is going to be at address 123 and the chip is going to be at address

123 and so at that address for the hundred ship. It's programmed to display a [1] at that address for the tens chip

It's programmed to display a 2 and the ones chip is programmed to display a 3 and then they go on to [say]

Let's say we want to [represent] the numbers from 0 to 15

We can use 2 [e] [eproms] and this is this is exactly right here, so this shows for the address 0 through 9

That first the eeprom is just outputting all zeros and the second one

Outputs the numbers from 0 [to] 9 and then it wraps around here

And that first year you promised a 4 10 through through 15

[sort] [of] kind of restates that and then says

if you link the address lines of the chips together so all the chips get the same address you put the binary number on the

The output of the chips will display the decimal : that's that's a yes

But then this is this is interesting the [YouTube] cuber again says another thing that I thought of is

multiplexing through the eeprom so you get the binary number and the digit number as input and

Then you get a you know binary coded decimal

Decoded set and segment [things] [as] your output and so you need a binary counter on the digit number input to [start] multiplexing

I like this idea rather than needing [to] have three of these [ee] problems one for each digit

We can do it with a single the eeprom that drives all three digits now

It's going to be a little bit more complex

But it's I don't think we're going to need to do anything that we haven't already done elsewhere in our computer build

So let's give it a try and I'll explain more about how those

Multiplexing works as we as we build out the circuit, so this display module is going to be part of our computer

It's going to [be] output for our computer

So I'm going to connect a new breadboard here right below the b register for a computer and build the display

Output here, and so we're going to use a single eeprom

that's the the idea of this multiplexing idea the 28 C 16 [I'll] start by connecting it to a

single [seven] segment display, and this is a

Instead of common anode which were the ones we were using before so I'm going to connect the common cathode here to ground

There is the reason I'm using a common cathode

Display here which I'll go into later and so I'm just going to check the eight output pins for the eeprom to the seven

segments of the of the seven segment display plus the decimal point

And it really is just kind [of] hard to follow with everything on top of each other there

But basically what's going on is we've got these i/o pins [io0] [one] [two] [three] [four] [five] [six] [seven]

Those are the pins that are connected here, and they're connected to the seven segment display

So you know this is what our seven segment display is going to do just zero through nine [since] we're just getting decimal at this

each of the segments it has a letter designator, so

Abcde F and then g is the one in the middle

And then of course there's also the decimal point over here, and so this is the way that I've arranged the the bit order

So the decimal point is the most significant bit so that corresponds

Abcdefg where g is the least significant bit corresponding with io 0 over [here]? So that's that's how I hooked this up

[but] of course you can hook it up any way you want you just got to make sure you know which bits need to be

On for each of the numbers that you [want] to display?

now we can also hook up power and ground for the eeprom so that [it's] powers and

Then the control signals that we've got we've got our chip enable our output enable and our write enable

And chip enable we want that to be active, so that's active low

Output enable we also want to be active, and that's also active low

Then write enable we don't want that to be active

We don't wanna be writing to this and so that's active low

So we want to tie that high so that we're not

Going to accidentally write anything to this chip and so that leads just the address line

So there's eight address lines over on this side, and then address eight nine and ten over on that side and for now

I'm just going to temporarily tie those all low

That's the first eight address lines are all tied low there and then I'll also tie the remaining three address lines over here

Low as well, so with all of the address lines tied low

This tip is going to be addressing address location zero and we'll see whichever bits are set on the output here

We can see that. We're getting all the bits set so all seven segments plus the decimal point are on so

Address locations, they're on this chip is apparently programmed with with all ones and if we go to some other address so address one

Two so it looks like this chip is probably erased if all it's giving us is all ones on the output

So let's pull the chip out in and program with something

So I've got the eeprom in our Arduino programmer

And I'm going to come over to the code here and because we're using a common capital display now instead of a common anode

I'm going to make sure I've got the [right] programming for that

So this is the right bit that we want to have set for common cathode

so I'm going to add and upload that and I look at my serial monitor, and so it's programming and

Okay, it looks like it's going to start by erasing the eeprom and then it programs it and it looks like it's got that program

In there for the first 16 bytes okay, so let's pull it out and put it back in our other circuit

to put this back in here now and connect power

So now we've got a zero and if we go to address location one. We've got a one and

but of course we want [to] have more than one digit and so [the] way the

Multiplexing is going to work is we're actually going to drive all the digits using the same data bits

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Build an 8-bit decimal display for our 8-bit computer

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