Name: Connecting an LCD to our computer — 6502 part 4
Uploaded: 2020-03-27T17:08:19.000Z
Duration: 28 min 10 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...

these little LCD modules are extremely common.

Gerund

But what to take to hook one of these up and get it working?

The imperative

Let's get these 16 pins that are used to interface with it.

So if we just feed the right signals in, we ought to be able to get it to do something.

And I got this little computer that I've been building that so far I've just programmed toe blink some lights.

But now, instead of using these signals, just attorneys led us on and off like this.

Let's use them to feed in whatever needs to be fed into this display to make it do stuff.

Let me get these ladies out of the way and I'll get the resisters out of here and I'll install one of these LCD modules and and these come in different colors.

I think it shows a little bit better in the video, but I'll start by hooking out power to the display.

These 1st 2 pins air for five full power and V s s is ground and then V tedious five volts.

It says the power for the module into the next pain here is V zero, and that's for adjusting the contrast of the display.

And really, all we need to do with it is tie it to ground through a resistor.

To set the contrast, we'll use a 10 K variable resistors.

We can adjust the resistance to adjust the display contrast and already got the ground line here.

So we'll hook 11 leg of this up to that ground and then the middle pin will hook over to the V zero input.

And now we should be able to just turn this and adjust the display contrast and the rest of the pins Here are just the signals that will have to hook up to the computers.

I own lines here in order to communicate with the display.

Here there's actually for the backlight for the display.

So the display lights up and a is the anode for the backlight led.

So hook that to five volts and Kay is the cathodes will hook that to ground, and we can hook this directly to five votes like this because the models already got a current limiting resister in it.

That led by putting too much current through it.

We hooked directly to five volts, and we still haven't hooked up any the signals.

So it's not gonna really doing do much yet.

But let's up hard on anyway, just to sort of make sure and the backlight work.

And, you know, we could check the contrast setting, too, so because that ought to work.

So this is this is obviously maybe too dark.

And if we go the other way, that maybe to light.

So if I kind of said it somewhere in the middle there, that's probably about right there in the middle.

So hopefully, if anything were on the display, we'd be able to see it.

But of course, you know we're not sending anything to the display yet, so you know it's probably good.

Let's look up the data lines so we can actually send data to the display.

You can see they're actually ate data lines here, so D zero through d seven.

It's all just hook up all eight of them to the 65 22 interface adapter here.

And I'm hooking these up to the same eight bits that I originally had.

Those led is hooked up to because we know we can set those pins to whatever one.

And you know, actually, I technically don't need to hook up all eight of these.

The display actually has a mode where you can do everything with just four data bits, which is a nice feature because it means, you know, we wouldn't have to hook up many wires or we wouldn't need to use as many pins on the 65 22.

But the A pit mode that I'm hooking up here is a bit simpler to use, so we'll start there.

But, you know, maybe if you're doing a project like this yourself and you know you could get all the parts over eater dot net slash 65 02 But you know, whether you get the parts for me, you're somewhere else.

If you doing a project like this, you might want to try figuring out for yourself how to do it with just four bits.

But the a bit mode is a good place to start because that is gonna be easier for us to use in.

Either way, there are also a few control signals that we need to hook up.

So this rs r w and e pins are additional control signals that we need along with the eight data lines.

Unfortunately, the 65 22 interface that were adapter that we're using has to eight bit i o ports that we can use.

So we could just hook up these three control signals to three more Io port pins over here, and we'll be able to control all the things.

So hook up this e pin, the art of you pin and the RS pin into those all the pens we need to look.

Well, we need to dive into the data sheet to figure out how this all works, and this is actually the data sheet for the interface chip on the module.

It's not the data sheet for the entire module, which, which actually means we don't really care.

About half of what's in here because on one side you were talking to the chip through this.

You know, the eight Data Signal's lost these control signals rs RWE that we just hooked up.

But the other side of the chip actually talked to the actual LCD screen, and so it's got a whole bunch of pins.

And so, you know, the chip itself has tons of pens that we don't really need to worry about, because most of them are these, like common and segment pins, they go off to the actual display and control, which pixels on the display or set.

And actually, the display they were using 40 by 16 isn't even enough.

So there's there's actually a little expansion ship here is well, and so there's extra pins that interface to that expansion ship.

But we don't have to worry about any of that because someone else has built this module and taking care of figuring that out.

So we can just ignore roughly half of what's in this data sheet.

Um and really just focus on this interface here.

An MP was microprocessor unit which, you know, we're building a microprocessor computer.

Then we see the eight data lines that we've hooked up a CZ Well, as the r S, r W and e signals that we also just hooked up.

And the way this works is we've got these eight data lines going in, and there's a data lines either access the data register, which stores eight bits of data or the data lines can access the instruction register, which also stores eight bits of data and the way we select whether we wantto send data to the instruction register or the date of register is with the register select signal.

That's that's what this RS is register select.

So if register select zero than any data we send in here is gonna go to the instruction register, And that might be where we send commands to initialize the display or clear the display or move the cursor around things like that.

But then, if register select is high than the data that we send goes into the data register and I would typically be how we send whatever characters we want actually appear on the screen, because then that goes into the data display RAM, which stores all of the characters that are currently on the screen.

There's also a read right signal, as we can actually read information from the display model to wear it just writing to it.

For example, we could read what's in the data registers to get data out of the display Ram or, you know, we could read with Register Select Low.

And actually, we wouldn't read the instruction register.

When Register Select is low, we actually end up reading the address counter a CZ well is the busy flag, so those come out as well, so there's data we can read and write, so we have a read right flag there.

And then finally, the the E pin is the enable signal.

So for any of the reading or writing we might do here they've been talking about the actual read or write doesn't happen until the enable signal is is toggled high.

So let's look at the assembly code we're using to control these signals.

Is the program ahead running and puts a pattern of 50 hex out on the eight bits that we had there and then he uses this rotate right instruction to shift the bit pattern over each time through this.

But first it initialize is the i o interface chip.

Just address 6002 is the data direction register that says whether these eight bits here on the right, that we're using our whether we're using this for input or output.

And so, by storing FF in that register, we're saying that the signals are all hell puts.

Actually, we could make this a little bit clearer by defining symbols for these different addresses.

So instead of just saying six years or two, we could define some symbols up here.

Is that address 6000 and port A, is it address?

Six year 01 And Port A is the eight bits on the left here.

So we're just gonna be using the top three of those bits, and then port B is the eight bits here on the right that we've got hooked up, but then in the code, Once we define those addresses here, instead of saying, store a six years or zero weaken, say store, eh?

Port B, This is the same as it was before, but hopefully maybe a little bit easier to make sense of.