A Personal View of the Atari 800 (May, 1982)
A Personal View of the Atari 800
by Roger H. Edelson
While the model 800 computer by Atari (Sunnyvale, CA) can be used in a small-business environment, this role is now being de-emphasized. In this system, Atari has managed to produce more of a personal computer, excelling as a combination game machine, interactive educational device, home information management system and fully programmable, general purpose machine. It is, primarily, a consumer-friendly system.
Its major shortcoming in the small business arena is its inability to run CP/M programs.
The system is based on the 6502 microprocessor integrated circuit and provides high resolution color graphics and sound. An RF modulator allows a user to select transmission on either television channel 2 or 3, depending upon which frequency is not active in the user’s area. If higher resolution display is required, the unit provides composite video output and sound. The system provides a full-sized, full-stroke typewriter-style keyboard packaged in a low-profile plastic case. The keyboard has 57 keys including cursor movement capability, and an additional four function keys are provided in a separate section to the right of the major keyboard. These keys allow system reset and selection of different game features. The SYSTEM RESET key is surrounded, top and bottom, by two fences to prevent inadvertent operation, which wipes the operating program. As a further example of the dedication to consumer friendliness, the ports on the lower front panel of the system, which are used to connect various accessories such as joysticks or paddles, are shaped so that it is impossible to insert the plugs incorrectly.
Once inserted, the plugs remain in place even during the most frantic game activity.
The system makes use of two busses: an internal motherboard arrangement that allows the mixing of ROM, RAM and special purpose modules; and an external bus that provides the method for attaching optional items such as the 410 program (tape) recorder, the 810 disk drive (the 800 can support up to four such drives), the 830 modem or other devices. If it is necessary to configure the system with a number of accessory devices, you will need the 850 interface module, which provides four RS-232C ports and one parallel port. Most of the devices that attach to the Atari through this external bus are intelligent, usually with an internal microprocessor, allowing simplified bus structure and control. One of the advantages of this external bus structure is that the accessory devices may be daisy-chained, and each device provides two cable sockets for just this purpose. There is a Catch-22, however; the program recorder, because it is not intelligent, must be the last device in the line and in some cases operation is unreliable in this position. To circumvent this problem, the recorder should be plugged directly into the computer, the program downloaded, the recorder unplugged, and the other accessories reconnected.
As part of the internal bus, the system provides two easily accessible slots (under the plastic cover) to insert ROM cartridges with various programs—either Basic or a growing number of assembly language games. The computer is human-engineered so that when the plastic lid is raised to allow either insertion or removal of the cartridges, the power is cut to prevent damage to the ROMs inside the cartridge. Another advantage is that this cover contains a fitted piece of aluminum that, when closed, forms part of an RFI tight enclosure making the computer neighbor-friendly. The system may be operated with its associated disk drive close to a portable TV with no interference. The internal bus allows expansion of the RAM memory to 48K bytes plus 10K bytes of system ROM, which may also be expanded with user-purchasable cartridges. One of the problems with the Atari bus is that it is not a true bus— the same signal lines don’t go to each card slot. Modules must be placed in their appropriate slots or damage to the computer or module may result.
Atari provides 16K-byte expansion RAM modules, which allow the system to reach its full 48K-byte capacity; other manufacturers supply a variety of Atari-compatible RAM cards with larger capacities. One advantage of these larger cards is that all spare slots are not used when configuring the computer for 48K bytes of RAM. One of these alternate cards provides an additional 128K bytes of memory, which may also be configured as an electronic disk, speeding disk I/O operations. While Atari does not specifically forbid the use of other manufacturers’ devices or modules, it does caution that certain items can overload the power supply. It is possible that your warranty will be voided by the use of these units.
The resident operating system ROM, which must be inserted in the first module slot, occupies the 16K-byte addresses from E000 to FFFF. The RAM occupies dedicated locations from 0000 to 7FFF (32K bytes), with at least 4K bytes (from 0000 to 1FFF) needed for minimum system operation. The cartridges (either Basic or other) and RAM share the locations from 8000 to BFFF—16K bytes first overlaying the right cartridge addresses and then the left. In case of an address space conflict, the cartridge disables the conflicting RAM in 8K-byte increments. When DOS 2.OS is in residence, the free RAM space is decreased by almost 8K bytes. The 6502, like most microprocessors (with the exception of the 8080/Z80 class), uses memory-mapped I/O, and the address from D000 to D7FF is reserved for these functions. The peripheral interface adapter is tasked with handling the joystick inputs, and in conjunction with POKEY (the digital I/O chip), takes care of the paddles and the main keyboard. The CTIA accepts inputs from the console switches, joystick triggers, data from ANTIC and sound from the POKEY chip, producing the composite video and sound for the RF modulator as well as sound for the speaker located in the computer. In addition to producing the video data, the ANTIC chip also takes care of the light pen.
Set-up is quick, easy System set-up is simple; plug in the AC adapter, attach the RF switch box to the back of your TV set with the double sided sticky tape provided, make the appropriate antenna connections, adjust your set and your computer to either channel 2 or 3, and go. With no cartridge inserted in the available slots, the computer comes up in the Memo-Pad mode, indicated by the white text ATARI COMPUTER MEMO PAD on a blue background, which allows writing text in 24 by 40 format onto the television screen. This is another example of the system’s consumer-oriented design— even with no cartridge, or loaded program, the computer does something. If the operator takes no action after a reasonable length of time, the computer will vary the screen colors to prevent damage to the television.
Upon power up, the computer will determine the highest RAM address, clear all RAM to zeroes, establish interrupt vectors and device tables, initialize any cartridges and set the screen to the text mode. Blackboard mode is the lowest priority environment (to use Atari’s term)—invoked only if the system cannot support a higher environment, such as Basic, cartridge or DOS. This mode can also be entered, if directed, from a higher environment (i.e. entering BYE while in Basic). Even in this minimal mode, the full-screen editing functions are maintained, though all text entered is written directly to the screen without examination. With the Basic cartridge inserted, there is a slight pause, and the computer will then respond with the word ready; at this point you can start to write, and run, Basic programs. The addition of the 410 program recorder doesn’t complicate this procedure much more—one additional line plug is added and the recorder is plugged into the external bus port. The computer controls the 410 recorder in the play mode starting and stopping the tape as required by the program.
Adding a disk drive (the single-drive 810 or the dual-disk 815) to the configuration begins to complicate the system both physically and operationally—a factor that limits the model’s performance as a small business machine. Each disk drive unit presents the user with another AC adapter/transformer to plug in. If you are planning to configure your 800 system with a 410 program recorder, an 810 disk drive, and possibly a printer (with the 850 interface module), purchasing a plug-strip to allow several plugs and AC adapters to be grouped as desired is recommended. One of several available switch/socket boxes that will also allow easy on/off control of each device can be used. To operate the computer with an attached disk drive, the drive must be turned on before the computer is powered-up and allowed to time out before inserting a disk—then the computer is turned on.
This operational sequence allows the disk drive to initialize itself and presents appropriate information to the computer when it examines the external serial bus to determine which accessories are connected. Once the drive has timed out (an LED indicator labeled BUSY lights up), the disk may be inserted and the computer powered-up. At this point, the system will configure itself dependent upon the computer configuration—with or without Basic or another cartridge and the disk program. The system may power-up with the DOS disk utility active, it may come up in the Basic programming mode (in which case the user may get to the disk utility by inputting “DOS” followed by “RETURN”), or the disk booted program may take complete control and begin running a program. As the system is so flexible, it is difficult to generalize about the power-up state. The only requirement is that there must be sufficient RAM to support the program being booted.
The disk utility features a menu-driven, consumer-oriented operating system that is self-prompting and easy to use. With this operating system, it is possible to format disks and transfer the operating system to those disks. The utility allows file transfer, or full disk copy, operations with either single- or multiple-drive system configurations. One can rename or erase a file and the directory command provides file size and available disk space information. The operating system and Basic allow operations with either random or sequential files, and the standard Basic commands such as OPEN, CLOSE, READ and INPUT are supported. The disk drive uses standard soft-sectored 5-1/2-in. diskettes, which can store up to 88K bytes each; some of this space is used for system software.
14 graphics modes are available The 6502 microprocessor operates at 1.79 MHz, one-half the standard television chroma oscillator frequency (~3.58 MHz), and provides a maximum resolution of 192 V by 176 H pixels—the maximum horizontal resolution can be 352 pixels. Through the use of the ANTIC graphics/video microprocessor, the 800/400 computer provides 14 different graphics modes (nine are available directly from Basic). Through the use of ANTIC, Atari computers excel in their sophisticated and flexible ability to handle video graphics. Using a technique called DISPLAY LISTS, one can display the machine’s full 128-color pallette and even manipulate these colors.
My system consists of an 800 computer, one 810 disk drive, the 410 program recorder, and an Epson MX-80 printer driven by the 850 interface module. To connect this to AC power, I use a combined RFI filter and switch box, which allows individual on/off control for each unit. I plan to design a device to automatically sequence the power to the disk drive and the other items to avoid the annoying operational sequence. The full-stroke keyboard has a nice feel to it, though care is necessary to avoid accidental depression of the reverse video key—identified with Atari’s symbol. The Basic is easy to use, though not quite as powerful as those available for my S-100 machines. When in the Basic environment, the programmer has available graphics commands such as DRAWTO, PLOT and POSITION, the ability to easily set the screen and display colors, plus control of four independent sound synthesizers.
My system is reliable and has given me many hours of enjoyable operation. The disk drive has performed without error in a regime that has included many file transfers and disk copies. With its flexible and comprehensive graphics and audio capability, the system ranks as a top-of-the-line personal computer. Its extensive peripheral array and software support make it an excellent choice for those considering a personal computer system.
Next month’s Hardware Evaluation will discuss the three accessories to the 800. □