Atari 800XL: We look, we sort, we include

    Surely many Habr readers grew up on ZX Spectrum and BK-0010/0011 computers, well, or at least came across them in the distant 90s. For many, these PCs have become the starting point in the IT world. But, like many other things, eight-bit home computers came to our country much later than the rest of the civilized world, and not in full. There, this era began almost 10 years earlier, in the late 70s, when Atari 400/800, Commodore PET and, of course, Apple II came out. The mass distribution of home computers began to get in the early 80's. In 1982, the famous ZX Spectrum 48 and the equally famous Commodore 64 were released, in 1983 the Atari 800XL was released, and in 1984 the first Macintosh appeared on store shelves. Like most home computers at the time, the Atari 800XL was based on a 6502C processor with a frequency of 1.79 MHz,




    0 Theory


    As I already wrote, the heart of the Atari 800XL is a 6502C processor, clocked at 1.79 MHz in the NTSC version and 1.77 MHz in the PAL version of the computer, respectively. But inside it was far from the only chip. 6502 came to the aid of the POKEY chip, which works with I / O devices and is responsible for the audio subsystem, and the chips that are responsible for the video subsystem, under the names ANTIC and GTIA. The ANTIC chip in conjunction with the GTIA allowed to significantly save RAM for displaying the image on the screen. In total, 64KB of RAM was soldered on the board. Of these 64 KB, only 37,902 bytes are available to the user. The rest of the volume was occupied by the BASIC interpreter. By default, at boot time, the contents of a ROM chip with a BASIC image are overwritten into RAM. The interpreter could be prevented from loading by pressing the Optio button during power-up. For obvious reasons, this operation required the completion of most games and applications. I will not bore you with large volumes of text, incl. We will consider in more detail everything upon receipt of visual information.

    1.Watch


    As you can see, the computer is a small monoblock, on the upper edge of which there is a QWERTY keyboard, a window for the cartridge slot. To the right of the main keyboard are the Reset, Option, Select, Start, Help keys and the power indicator next to it. The Reset key is used for the so-called Warm Reset, but if "everything is bad" and you need a full reset, you will need to reach for the power switch on the back side.



    The keyboard is made on the basis of hybrid mechanical-capacitive switches. When pressed, the spring compresses, which causes a change in capacity and leads to a response. The keys have a very soft and silent stroke. Now this type of keyboard is called Topre.



    Rear panel. The main ports of the device are located on it. On the left is the SIO (Serial Input / Output) port. In my opinion, this is one of the most remarkable things in Atari 8-bit computers: this standard made it possible to sequentially connect more than 10 devices to a computer without any problems. Atari SIO was developed by engineer Joe Decuir (an interesting fact: Joe also participated in the development and has some patents for the USB standard). Next, under the stub, is the parallel port. It was used to install extensions. Such as Atari 1090XL Expansion System chassis, memory extensions and some other modules. We’ll look closer at it while disassembling the device. Next is the A / V port, nothing unusual here. A little further - RF plug. Next to it you can see the sealed hole of the TV channel switch, it is present only in the NTSC version. Next is the power connector and the power switch.



    On the right side are the ports of the joysticks. I could not find a native joystick, but as many know, the joysticks from the Sega Master System and Sega Megadrive use the Atari standard. T.ch. a two-button joystick from the Sega Master System was very helpful.





    The computer is powered by a weighty power supply with a voltage of 5V to 1.5A.



    And now a small comparison with the ZX Spectrum local spill. As you can see, the dimensions of the devices are almost identical.



    2.Disassemble


    We turn off 6 screws and the first thing we see is a massive screen that covers almost the entire board. Metal is screwed directly to the board with screws. On the right is the keyboard loopback port.



    Surprisingly, the cartridge flap is also a screen. These days you will not see this.



    Turning the board over, we see a no less massive screen. We turn it off.





    Unscrewing the top screen, we see all the most interesting. All the chips are in full view.



    For convenience and satisfaction of readers' curiosity, all the chips were signed by me, but for even more curious there is also the original high-resolution photo. The architecture of 8-bit Atari computers is very different from the ZX Spectrum, in which all functions are assigned to the Z80. For this reason, copying Atari computers was extremely difficult, which led to the lack of popularity in our country, like many other foreign computers.

    Take a closer look at the chips.







    3. Launch


    First of all, finding the pinout of the video port, I stuck the bare wires into the port and ran to the nearest radio components store, bought a DIN connector, soldered the plug for the A \ V wires with the usual tulips on the other end, connected the whole thing to the tuner and enjoyed the blue screen with the READY inscription on her. The blinking cursor clearly beckoned to type on the keyboard a couple of lines of code on BASIC, which I did. Immediately a little surprised by the process of editing the code, namely: display the program listing, move the cursor to the right place and edit. For clarity, imagine how you, after entering the ls or dir command, move the cursor to the list of files and rename them right there. Oddly enough, a new line in the code is added by the insert key.

    Basic


    Having played enough with BASIC, I loaded 800XL into test mode, which, as I said, is also wired into its ROM memory. This software does not represent anything particularly interesting, you can check the operation of the keyboard, audio subsystem, check the integrity of the ROM and RAM memory. The last procedure takes quite a long time - more than 10 minutes. Our veteran successfully passed all tests.

    SELF TEST


    My next goal was the so-called SIO2PC adapter, which allows you to connect the SIO to the computer's COM port and emulate up to 15 devices. This makes it possible to connect a couple of virtual drives to our Atari and load into them any possible images, to read / write. You can even print text on a printer and emulate a cassette drive! Interesting? So I was extremely eager to run at least some disk OS on 800XL and enjoy the masterpieces of the demo scene live.

    The adapter itself is a simple logic level converter COM-> UART. I used the MAX232 chip that came to hand, the circuit is quite simple, it is easily soldered to the breadboard. But I had problems with the wire, it had the wrong wiring, and did not have a wire for the ninth pin (Ring Indicator), which is used to coordinate devices.

    SIO and DIN board during soldering


    For convenience, it was decided to cut off one end by soldering the necessary wires directly to the board, and on the other end to solder the unnecessary and solder to the RI pin. The SIO plug itself is completely non-standard and it will not work to buy something suitable in the radio store, so it was decided to use simple pin connectors.



    After a simple setup of software for emulating devices, our piece of hardware happily started from the image of a floppy disk downloaded from the network. A menu appeared on the screen with a choice of loading several OSs at once. In my opinion, the most convenient, oddly enough, turned out to be something called Happy Computer II + / D. I won’t go into details, various versions of any DOS for 8-bit Atari PCs are just a sea. I can only say that along with the disk manager, device drivers are loaded into RAM. Many disk OSs are loaded with support for only 2 input / output devices (which is quite logical), but managers like Happy Computer and Sparta DOS support up to 12 disk devices, which turned out to be extremely convenient in my case. In general, all of them are very similar to regular MS DOS, with the exception of the native Atari DOS 2-2.5,

    Disk OS




    And of course the game! And there are a lot of them made for 8-bit Atari computers. The largest archive of games I found totaled more than 6,700 of those. In general, in terms of quality, many games have not gone far from the Atari 2600 with its angular graphics, but there are also samples worthy of attention. For example, I was very impressed with the game Encounter. Pseudo-3D and dynamic gameplay dragged me into the game for almost an hour. In the game, we need to control some kind of tank spaceship and destroy alien guests, although you can dream up what your heart desires.

    Zerro and Encounter Games



    And where without demoscene? It is very voluminous on Atari, hundreds of demos with wonderful graphics and music have been made. Programmers pulled all the juices from the 6502 processor and the POKEY chip. Several demoscenes were recorded by me directly from iron and are in the section below, I highly recommend looking at them. Also on pouet.net presents a huge number of different demos of varying degrees of coolness. A direct link to the section of the site will be below.

    4.Video




    Atari 8-bit power

    * This demo is made by Atari itself. It was demonstrated in stores on display cases.

    Dos OS


    Encounter


    RGBA Demo


    5.Links


    Atari 8-bit family Eng Wiki
    Atari section on zx-pk.ru
    Atari XL / XE section on pouet.net
    Large archive of applications and games on rutracker
    Customized Altirra emulator + disk images and applications described in the article
    ASM MADS
    Cross Compiler Cross Compiler Effectus AspeQt
    Device Emulator (SIO2PC)

    Thank you for your attention! I hope it was interesting.

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