An advertising manager I know once joked that "today's product flaws are tomorrow's features." According to this definition, ATARI home computers are among the most feature-packed on the market. The 400/800 operating system in particular is full of quirky little "features" which 3rd-party suppliers have been successfully exploiting for years.
One of the most interesting flaws in the OS is the wasted 4K memory bank located at hex $COOO. OMNIMON!, a new hardware product from CDY Consulting, replaces this otherwise useless memory area with a powerful ROM-resident system monitor, similar to the one included as standard equipment on other popular micros such as the Apple II.
OMNIMON! is entered by pressing SYSTEM RESET while holding down either the OPTION or SELECT key. You can also activate it with a USR call out of BASIC, or by executing a JSR $COO1 instruction in machine language. Once "inside," you can examine, search, disassemble and alter memory locations, monitor the 6502 registers and hardware stack, read and write individual disk sectors and keep printed records of your work. Best of all, you can access these functions whenever the computer is turned on, regardless of what other software may be running (including a cartridge).
The screen photo shows the OMNIMON! title display and a menu of all available commands. The menu can be reviewed at any time by typing the "?" character, a thoughtful touch which typifies the friendliness of the system. All of the most-needed monitoring and debugging functions are available. Many are reminiscent of those included in the ATARI Assembler/Editor cartridge.
The disk I/O commands are the most interesting part of the OMNIMON! system. They allow you to read any specified range of disk sectors into RAM, using either the 128 byte/sector boot format or the 125-byte/sector DOS format - in either single or double density mode! This means you can load and execute binary DOS files without using a DOS. OMNIMON! also lets you convert DOS files to boot files and vice-versa, a capability found only in the most expensive software-based disk management programs. Other possibilities include dumping any block of RAM, OS or cartridge ROM out to a disk and moving it back into RAM anywhere you like.
OMNIMON! checks the syntax of all user inputs and reverts to reasonable defaults if no parameters are specified. All of the ATARI's built-in screen editing functions are supported; you can use the "T" (Toggle) command to enter data in either hexadecimal or ATASCII characters.
It took less than five minutes to get OMNIMON! up and running on the 800 system in my office. First you pop open the lid, pull out the personality board in Slot #1 and discard its plastic cover. Then you pull out one of the CIS ROM chips and plug the L-shaped OMNIMON! board directly into the empty socket. Solder a single jumper into place, replace the CIS chip and personality board and you're ready to go. OMNIMON'S 16 page user's guide includes complete installation instructions for both the ATARI 800 and 400 computers. It cannot be used with the 1200XL system.
The OMNIMON! board has behaved itself fairly well in the several weeks since I installed it. It appears to be fully compatible with all of the ATARI programming environments I tested, including the BASIC and Assembler/Editor cartridges, Microsoft BASIC, the ATARI Macro Assembler, OSS BASIC A+ and MAC/65, the ABC BASIC compiler and vaIFORTH.
I did run into trouble with a couple of copyprotected game disks. For instance, my review copy of Pinhead by Utopia Software refuses to boot properly on my modified 800; instead of initializing the game, the system makes a gurgling noise and jumps into OMNIMON!. A similar thing happens when I try to use Disked by Amulet Enterprises. Every time I answer a sector number prompt, the system drops out of BASIC and into OMNIMON!.
It's hard to say whether this behavior is being caused by the OMNIMON! board or by the offending software itself. The rarity of the phenomenon suggests that the programs are making illegal entries into the ATARI's resident disk handler, thereby interfering with OMNIMON!'s hooks into the operating system. This is similar to the problem owners of the new Apple IIe system are having with disks that were copy-protected for the older Apple II and II+ systems. The moral in both cases is the same: Avoid non-standard OS calls!
OMNIMON! can be a great addition to your ATARI computer if you know what to do with it. The ability to "freeze" a running program on-the-fly and examine the hardware registers is invaluable for testing and debugging; the sector-level disk functions are alone worth the price of the board. If you do lots of machine-language programming and know which end of the soldering iron to hold, OMNIMON! might be one of the smartest hardware investme you can make. Look for it at your local CDY dealer.