Unlike my floppy drive box, only a single goat has pissed on my PCjr box
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Code running out of the ROM , like the BIOS, and any cartridge you might have plugged in before everyone gave up on that idea, was also fast.
Tandy, when copying the PCjr to make the Tandy 1000, looked at this and saw that it was bad.
The Tandy 1000 also has a 128K window of shared DRAM, but they did two things to make the Tandy 1000 not terrible.
First, they shuffled some stuff around and tweaked some timings and basically halved the number of wait states required. Yay!
Secondly, they made the 128K shared window configurable - the system would normally move it to the top of RAM, where you were less likely to need to run code out of it, especially important stuff like DOS. Yay!
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Tandy, when copying the PCjr to make the Tandy 1000, looked at this and saw that it was bad.
The Tandy 1000 also has a 128K window of shared DRAM, but they did two things to make the Tandy 1000 not terrible.
First, they shuffled some stuff around and tweaked some timings and basically halved the number of wait states required. Yay!
Secondly, they made the 128K shared window configurable - the system would normally move it to the top of RAM, where you were less likely to need to run code out of it, especially important stuff like DOS. Yay!
On some later Tandys you can even install a whopping 768K of RAM and have the 128K of video memory live up there above the 640K boundary and have your cake and eat it too.
There was a lot of cool stuff the VGA/TGA could do. I mean, being able to instantly switch to rendering graphics anywhere in a 128K window was a pretty crazy cool feature when you think about it - the CGA only had a measly 16K of video memory by comparison.
Unfortunately, nobody was going to make a game that relied on that, because your game had to work on the PC if you actually liked, you know, making money.
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@gloriouscow
It's a good thing that a "Tandy" "Gate Array" doesn't have any other meanings either, nope none at all...@TechTangents so much future Tandyposting to do
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On some later Tandys you can even install a whopping 768K of RAM and have the 128K of video memory live up there above the 640K boundary and have your cake and eat it too.
There was a lot of cool stuff the VGA/TGA could do. I mean, being able to instantly switch to rendering graphics anywhere in a 128K window was a pretty crazy cool feature when you think about it - the CGA only had a measly 16K of video memory by comparison.
Unfortunately, nobody was going to make a game that relied on that, because your game had to work on the PC if you actually liked, you know, making money.
Shall we see if my peanut even boots?
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Shall we see if my peanut even boots?
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The IBM PC uses the 8253 timer and 8237 DMA controller to refresh the system's DRAM. The D in DRAM stands for Dynamic and dynamic means if we do not refresh the RAM by accessing it periodically the contents go bye-byte.
Doing this saved IBM a decent amount of money on making dedicated refresh circuitry, at the cost of about 5-6% of your CPU performance.
@gloriouscow The 8257 is pretty mid, good thing IBM used the somewhat better 8237.
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@gloriouscow The 8257 is pretty mid, good thing IBM used the somewhat better 8237.
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I'm currently having all the wireless IBM Keyboard Adventures, and you're not. Jealous?
I'm sitting about ten feet away from the peanut and the keyboard seems to work just fine. Although, this is a fresh set of batteries, and it's relatively dim in here because I live like some kind of techno-troll.
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@gloriouscow The 8257 is pretty mid, good thing IBM used the somewhat better 8237.
@crazyc you ever consider how many neurons you're using to remember intel peripheral chip numbers
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I'm currently having all the wireless IBM Keyboard Adventures, and you're not. Jealous?
I'm sitting about ten feet away from the peanut and the keyboard seems to work just fine. Although, this is a fresh set of batteries, and it's relatively dim in here because I live like some kind of techno-troll.
obviously there's zero authentication to an IR keyboard.
it would be fun to make a tiny little emitter that could send text to a PCjr and then find the next person exhibiting one at VCF and send them messages from a few tables over.
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@crazyc you ever consider how many neurons you're using to remember intel peripheral chip numbers
@gloriouscow Lets talk about the 8274, 8256 and 82720. Or better, lets not. (the 8256 is required to emulate the Philips :Yes and I don't wanna do it)
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obviously there's zero authentication to an IR keyboard.
it would be fun to make a tiny little emitter that could send text to a PCjr and then find the next person exhibiting one at VCF and send them messages from a few tables over.
IBM mentions in passing in the technical reference that you could make other IR accessories for the system, but it was up to you to figure it out and the timings were tailored around the keyboard.
I'm not sure if anyone ever did - at least I'm not aware of any 3rd party IR accessories.
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IBM mentions in passing in the technical reference that you could make other IR accessories for the system, but it was up to you to figure it out and the timings were tailored around the keyboard.
I'm not sure if anyone ever did - at least I'm not aware of any 3rd party IR accessories.
There's a fun video of LGR experiencing some ... issues with his PCjr IR port.
The beeping was an intentional feature by IBM to inform you that you had a bad keyboard signal. A beep occurs if the system receives a parity or phase error.
"I hate and love you so much" is something that I feel deeply
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There's a fun video of LGR experiencing some ... issues with his PCjr IR port.
The beeping was an intentional feature by IBM to inform you that you had a bad keyboard signal. A beep occurs if the system receives a parity or phase error.
"I hate and love you so much" is something that I feel deeply
- YouTube
Auf YouTube findest du die angesagtesten Videos und Tracks. Außerdem kannst du eigene Inhalte hochladen und mit Freunden oder gleich der ganzen Welt teilen.
(www.youtube.com)
Because I am very normal I needed to see if I can read the PCjr keyboard IR protocol with a light pen.
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Because I am very normal I needed to see if I can read the PCjr keyboard IR protocol with a light pen.
The IR signal is biphase-encoded. You can't really have the IR blasting all the time, and an absence of light isn't meaningful either, so quick pairs of light pulses signify meaningful data.
The first pulse is always 1, being the start bit. The start bit establishes the beginning of a series of 9 windows to follow, called bitcells. If a pulse appears at the start of a bitcell, it is a 1. if a pulse appears in the second half of a bitcell, it is a 0.
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@gloriouscow
Yes. It definitely will. -
The IR signal is biphase-encoded. You can't really have the IR blasting all the time, and an absence of light isn't meaningful either, so quick pairs of light pulses signify meaningful data.
The first pulse is always 1, being the start bit. The start bit establishes the beginning of a series of 9 windows to follow, called bitcells. If a pulse appears at the start of a bitcell, it is a 1. if a pulse appears in the second half of a bitcell, it is a 0.
The scancode is sent LSB first, after a start bit, and a parity bit follows.
So our scancode is 0b0001_1110 or 1E.
What key is that?MartyKey::KeyA => Some(0x1E),It's A! So, I assume that if I wire up the light pen to the keyboard port, we can use it as an IR receiver.
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The scancode is sent LSB first, after a start bit, and a parity bit follows.
So our scancode is 0b0001_1110 or 1E.
What key is that?MartyKey::KeyA => Some(0x1E),It's A! So, I assume that if I wire up the light pen to the keyboard port, we can use it as an IR receiver.
This shouldn't really be a major surprise to anyone, considering the light pen is essentially made of the same things - a photodiode and some filtering circuitry.
But it's just stupid enough to make me happy.
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