PDP-1 programming: Mike Hill's Blinky program (and 'book'!)

Hinzugefügt: 2026-05-08

[00:00:21]read from blinky.

[00:00:24]Now we can mount this paper tape. We'll also turn on the audio output right now because Blinkck is capable of using the audio as well. Don't have to, but it can.

[00:00:36]Um, and now we'll switch to full screen because we don't need any output at all from Blinky.

[00:00:44]Okay. Now to start the tape reading in, which we won't see now, which is a shame. I'll I'll put it back here. We can see the tape reading in down the bottom of the screen perhaps.

[00:00:56]Once it's finished reading in, it's reading in three separate blocks, which is why there's some gaps in there. Okay, now I can switch to full screen.

[00:01:06]And we can start playing with Blinky.

[00:01:09]Um, Blinky has lots of features, but the best is the uh or the most interesting is perhaps the Easter egg, which was by making one, three, and five.

[00:01:24]And as soon as Blinky sees this, it switches into Easter egg mode. Now, we can set the speed here.

[00:01:31]I'm making it a little bit slower so we can see what Blinky is doing. And here it's showing its own recode in the accumulator and it's showing a delayed complement of the binary code in the IO register.

[00:01:47]And also if I switch on this, we'll see it's starting to display random dots, but those are just based on the information that's coming out of these two registers.

[00:01:59]So the X register is the accumulator, the Y register is the IO register, and it's picking different bits out of that to make a random pattern on the screen.

[00:02:09]And if I now switch to one of the uh second Easter eggs, which are Easter eggs to display on here, then I can choose um uh let me see.

[00:02:30]Turn this off and back on again.

[00:02:35]Now we've switched to rocket mode.

[00:02:39]But I can choose something different.

[00:02:42]For example, um maybe no, I won't bother. There's there's half a dozen different patterns that it can show here. But now I'm going to show you the nested chaotic Easter egg which is based on an algorithm by Marvin Minsky.

[00:03:01]And I can do that by switching uh let me see the switch off.

[00:03:10]Nope, not that one. This one. That one.

[00:03:12]There we go.

[00:03:14]Okay. And these switches here would also change that. And if we had the light pen enabled, we could change the display by clicking on different parts of that pattern.

[00:03:33]If the pattern is here and we go back and do the same thing.

[00:03:39]So we're seeing different patterns here.

[00:03:47]By choosing sensible values, we can get a circle or a relatively good circle.

[00:03:57]So what we're doing here, we're just programming an instruction. So it's programming a rotate instruction with different values.

[00:04:10]And if I now turn them all off, it'll go up to a perfect circle.

[00:04:19]Now we're back to the uh normal mode.

[00:04:22]And this is the default. If all the switches are off, it chooses a default value.

[00:04:28]And uh turning on four and five. So, one, two, three, four, and five.

[00:04:37]We're now not using the default values, but we've set the pattern the same. And the speed is now set on these three switches here. So, I can slow it down a bit or quite a lot or just a little bit.

[00:04:53]You can hear the pattern being played here.

[00:04:59]So if I change switch three 0 1 2 3 to the other pattern, you'll hear it changes the sound.

[00:05:10]Get a little horse.

[00:05:13]If we change it back, that's basically it.

[00:05:21]There are dozens of other things you can do with these switches here. For example, I can turn those two off and turn this one that one on.

[00:05:39]And you'll see also the overflow flag flashes at the same speed as the basic clock, which is these three switches here. That's the basic clock speed, and that's how fast that one will flash.

[00:06:01]That's all there is to it really. Can you show us some more of the Easter eggs? Maybe just for fun.

[00:06:05]>> That was all the Easter Well, no. That wasn't wasn't all the Easter eggs. There are plenty more. Okay.

[00:06:12]So, let's start here with one, three, five.

[00:06:20]Now we've got the basic U blinky showing you its source code or it's binary code seven.

[00:06:31]>> So it's a bit slow slow enough for us to see something but there's no output on the display right that's correct because if I do that >> exactly >> you'll get a different picture here every for everything it's showing here.

[00:06:45]Yeah the picture will be different.

[00:06:47]Okay. So, let's try um 33.

[00:06:55]Oh, not that one. Uh 135 13 six. Let's try 136. So, one, three, one.

[00:07:25]One, three, two, one.

[00:07:48]Okay, now we've got the base of rockets.

[00:07:51]It's guided missile though. So, okay, I beg to differ. I wrote the code. It's mine.

[00:07:58]Let's check set this to seven. It's a little bit faster.

[00:08:03]Okay. So, now we've got uh 135007 setup.

[00:08:09]And if we change that to 13 six, no sorry 131 07.

[00:08:16]1 3 1.

[00:08:20]Then we get a whole bunch of rockets.

[00:08:23]Now we can change it to 133 where we're getting what I call satellites. We can change it to 132. So 13 two.

[00:08:40]And those are called missiles or 136.

[00:08:46]One 36.

[00:08:50]That's just one missile.

[00:08:52]137.

[00:08:55]1 37.

[00:08:59]The dots. One, two, seven. One, two, seven.

[00:09:05]That's sky streaks.

[00:09:09]Okay. One. Someone have to come up with names.

[00:09:11]>> Uhhuh.

[00:09:12]>> One, two, six.

[00:09:17]And that's fireworks.

[00:09:20]One, two, two. One, two. Oops.

[00:09:25]Two. Oh, >> we're back there. I didn't want to be there.

[00:09:42]Three, five.

[00:09:47]Okay.

[00:09:50]And one, two, six, I think. Oh, no. I did all I did everything. That was it.

[00:09:55]>> Maybe we can show the the built-in help text because you're working from the cheat sheet, but the cheat sheet can be printed on.

[00:10:01]>> Absolutely. We can show that. Let's uh restart everything.

[00:10:07]First of all, we have to press the stop button as well. Now we can mount tape again.

[00:10:15]The same tape.

[00:10:17]And we can have to put the switches on first, right? Oh, yeah. Sure. So, if we switch on sense switch number three, uh, no, sorry, sense switch number four, then this will show the help text. The only time it will show it is when we're starting it because it uses the same memory twice, >> right?

[00:10:37]>> We overwrite ourselves. So, let's turn everything back off again.

[00:10:43]Okay. So, now we can Well, I've mounted the tape, I believe.

[00:10:46]>> Yep. So, I can just press read in where it will read in read in the code.

[00:10:54]So, it's now reading in the same code as before.

[00:10:58]That's the second segment. This is with the help text. The third segment when you see a gap would have been that. And now it's showing up the uh >> the blinky help text. And that's also why it's not the default option because it takes some time to type.

[00:11:10]>> This is what I've got on the cheat sheet in front of me.

[00:11:12]>> Yep. Let me zoom into that wobbly camera. But here you see the typewriter.

[00:11:21]And if you give it enough time at 10 characters per second, >> it will show that >> you get this. So that's why it's not the default startup option because before you get to Blinky, you have to wait too long. All right, Mike. Thank you very much.

[00:11:34]>> You're welcome. We can show you one more thing.

[00:11:36]>> Oh, yeah. Of course.

[00:11:37]>> If I set the switches to seven, seven, seven. Well, I have to turn this off.

[00:11:42]You can abort text by just turning it off, >> right?

[00:11:47]Then it will flash.

[00:11:49]>> Oh, yeah. Yeah. Yeah. The flashy thing.

[00:11:50]Yes.

[00:11:51]>> Yeah. So this is the flasher which we can change the speed of can't remember how many switches are speed but these are these are the speed switches for how fast it should flash.

[00:12:09]>> Right.

[00:12:15]So there you go.

[00:12:21]That's it.

[00:12:21]>> Thank you.

[00:12:22]>> You're welcome.

[00:12:23]>> That's what's hidden behind Blinky when you boot up. Not many people know that.