The TI 99-4A. (home computer) (evaluation) Fred Gray.

The TI 99/4A

In the beginning there was TI. And it was big and strong and mighty in the ways of digitals. It had The Watch, and it had The Calculator, and it made more chips than Frito-Lay. But other companies not as big and strong had home computers and were selling them like twinkies. TI looked in its parts drawer and saw a wondrous 16-bit microprocessor that it was most pround of. "We shall make a Home Computer,' said TI, and did so.

The TI 99/4 came out in 1979, was small, had calculator buttons for keys, and cost a lot. "See!' said TI, "we have a home computer!' "Hooray!' said the others, "You have a bomb!' And they were right and they were wrong. For the home computer was not a hit and sold like cold cakes, even when the price dropped from Apple Sky to Cheap City.

But under the funny keyboard was a mighty machine with dazzling color graphics and the 16-bit soul. TI looked at the sales figures and said to the engineers: Fix the fool thing and make it live up to the genius inside. And so they did. And so it does. And look out, others.

There were many things wrong with the TI 99/4 when it hit the street. It was much too expensive, it had a calculator style keyboard, it could run only Basic or plug-in modules, and had no expansion capability. These were not oversights, and TI had reasons. The cost was high because it was a new generation of machine and a color monitor came as part of the package. The keyboard came from the TI calculator heritage and allowed the use of slip-on overlays to redefine the keys for special modules. The machine was designed as a home appliance and the home user was not seen as being interested in fancy assemblers or exotic languages. Finally, to keep it compact and easy for the home user to use, there was no provision for slots or expansion board space; instead, peripherals and expansions were designed into silver boxes to be plugged into the side of the computer.

The price didn't stay high for long. It dropped from $1100 (with mandatory monitor) to under $500 (without it) by the end of 1980. The Basic on board was a good one, full of error-checking and editing capabilities, and considerable graphics capabilities. But the graphics capabilities were slow, too slow to allow anything exciting. True to their promise, TI did bring out expansion modules in silver boxes to plug into an ever-expanding daisy chain at the right side of the computer.

Chief among these was the Solid State Speech box, which gave the 99/4 300 words of highly understandable speech and made it, for a while, the only home computer that could talk.

Still, the 99/4 did not sell, a fact that may have been due to the philosophy of the TI hierarchy. Because the TMS9900 is an unusual microprocessor, and the 99/4 an unusual microcomputer with quite different architecture and I/O, TI decided to leave the fancy programming to their own staff, or to selected large organizations such as Scott, Foresman and Milton Bradley. So they did not publish anything about the workings of the machine and did not offer an assembler, and anyone wishing to do whizbang graphics or anything fast had to get a minicomputer development system, which cost about $50,000.

The result was predictable: practically no one wrote anything for the 99/4. And because the internal workings of the 99/4 were inscrutable and undecipherable, practically no one made any peripherals for it. While creative souls at TI were working hard on modules and peripherals, there were thousands of creative souls among the Great Unwashed who were writing Adventures and Starfights and making superboards and widget controllers for Apples, Pets, and TRS-80s. But not for the 99/4.

To their credit, the folks at TI woke up and have rectified virtually all of the problems of the 99/4. The 99/4A is all the 99/4 should have been and more, and now the machine is easier to exploit than ever before.

Hardware Improvements

Let's look at what is different about the 99/4A.

Of course, there is the new keyboard, a sturdy professional one that looks like a computer keyboard. It has a bunch of new keys, offers braces, square brackets, and lower case. It allows any key to be repeated at will, and allows keys to be used in three ways: key, shift key, and function key. Add to this the retained capability to redefine all of the keys through software and the ability of programs to search the keyboard during a run, and you have a most impressive input capability. All that is really lacking is a number pad for quick input of numerical data, which wouldn't have fit on the case.

But there are other changes, deep in the chips and ROMs. One is the use of the TMS9918A Video Display Processor (VDP) in place of the older 9918. To go with it is a revised operating system in ROM that opens up some of the advanced capabilities of both it and the 9900 microprocessor itself, as well as allowing the use of the expanded keyboard.

The TMS9918 is worth a side trip by itself. The VDP is an extraordinary display processor, able to display ASCII characters or user-defined characters in 16 colors on a 24 by 32 grid. More than that, embedded in the chip is the ability to display and move graphics characters called sprites, which can move smoothly across the screen and which, once set in motion by the calling program, continue to move at the specified speed and direction without CPU attention until changed by the program.

The VDP creates and moves the sprites based on data stored in the VDP RAM area by the program. By changing data, the sprites can be made to change course, shape, speed, color, vanish, or appear. The sprites afforded an incredible game and moving graphics capability to the 99/4, but because the internal Basic did not support their use, the capabilities were limited to plug-in modules, and not available to the home programmer.

The sprite capabilities of the Computer were opened up through the introduction of Extended Basic, available for both the 99/4 and the 99/4A. This module, adding some 36K of ROM to the on-board Basic, corrects many of the annoying limitations of the original Basic and opens up a wide range of additional capabilities to the machine.

With Extended Basic, the programmer can create sprites in two sizes, set their initial shape, location, velocity, direction, and color; change any of these at will; detect coincidences of sprites with each other or with specified points; change their size and make them vanish or become invisible--all with a simple call to one or more predefined subprograms.

Because the VDP does the work, the main processor is involved only with initiating the action, and the sprites will move as set while the 9900 processor is busy computing other things. Heavy computing by the CPU has no effect on the moving graphics as long as the motion doesn't change, and wild motion on the screen has no effect on the work of the CPU. Since up to 28 individual sprites can be defined and set in motion, the capability for dazzling color animation and games is almost unmatched in the home computer field.

The 99/4A adds another dimension to the sprite graphics not available on the 99/4, bit-mapped graphics. This highresolution mode is attributable to the 9918A VDP, and provides the capability to do bit-mapped color graphics on a 256 by 192 grid. Now the TI has highresolution graphics in addition to the sprite capability. Unfortunately, the bit-map mode does not allow the automatic movement feature of the sprites to exist along with the high resolution capability, as the VDP gets a bit overworked. Even with this limitation, the capabilities are astounding. We should see some amazing game and graphics programs soon.

Another capability of the TMS9900 microprocessor has been opened up for the 99/4A through a change to the ROM-based operating system. This is the ability to define up to 16 operations at the assembly level that can be used just as if they were added opcodes for the processor. The effect is to extend the instruction set by 16 and turns the new Assembler/Editor into a Macro Assembler. The ROM change did not take effect with the first bunch of 99/4A units, but is incorporated in the ones coming off the line now.

Editor/Assembler Package

The new Editor/Assembler module is now available for the 99/4A. From a review of the manual I can report that this module plus disk set is an extremely powerful software tool--in reality a minicomputer assembler in microcomputer form. TI has taken their assembler, editor, and linking loader packages developed for the 990 series minicomputers and reshaped them for the 99/4A. This was made possible by the fact that the 9900 and 990 instruction sets are virtually the same. Some of the remarkable capabilities that the Editor/Assembler brings to the microcomputer field are these:

Writing of relocatable, linkable code. The programmer does not need to worry about absolute addresses and can write his programs as independent subprograms to be linked together later by the loader. By defining certain labels as external references, the loader can match them up and link the programs together, filling in the addresses at load time. This also allows the loader to put the programs into memory wherever they fit best and not be constrained by the present configuration. The computer begins to look more like a minicomputer here. The great advantage for the programmer is the ability to write a library of subrountines, keep them on disk, and bring them into his programs as they are needed without worrying about the addresses or linkages.

Extraordinary editing capabilities. The Editor is very complete and offers a wide variety of conveniences for the programmer. Some of these are: inserting and deleting characters, inserting and deleting lines, copying whole blocks of code and inserting them elsewhere in the program, moving whole blocks of code around, searching for strings with the option to replace each occurrence with a new string, and a variety of filing commands. The system looks rather like a word processor for assembler code. It makes coding a great deal easier by removing much of the nuisance work.

Links to Utility Routines. TI has a great variety of utility routines tucked away in both ROM and GROM that are used by the operating system and the interpreters. Access to these routines makes it much easier to do the complicated graphics, sound, and speech routines. The programmer need only load certain parameters in the registers and then call on the utility routine to do the work. This capability is particularly needed with the graphics routines, as this area is rather inscrutable anyway. The utilities give the programmer the ease of programming exhibited by the Extended Basic while allowing the speed of machine-assembled code.

In summary, the TI 99/4A finally lives up to the promises of its makers. With new software and hardware improvements, the TI Home Computer is finally a powerful force in the microcomputer field and should not be counted out. At a normally discounted price of under $300, the 99/4A is an astounding value and may yet make its mark on the microcomputer world.

Products: Texas Instruments 99-4A (computer)