The system supports four RS-232 ports and two parallel printer ports. All device access uses a generic file-based I/O mechanism, allowing new devices to be added without updating software. When a new peripheral is attached, it is immediately available for any software that wants to use it. Access to this memory has to use the VDP as an intermediary.Īll TI-99 models have device drivers built into ROMs in the hardware. VDP RAM is the largest block of writeable memory in the unexpanded TI-99/4A architecture, and is used for storing disk I/O buffers and Each sprite is either 8×8 or 16×16 pixels and can be scaled 2x to 16x16 or 32x32.ġ6 kB of RAM is provided for the Video Display Processor. There are 32 single-color sprites total, but only a maximum of 4 can be displayed per scan line. The TMS9918A supports character-based and bitmap display modes as well as hardware sprites. It serves as the video processor for the ColecoVision and SG-1000 consoles, and an earlier model is part of the MSX computer standard. The VDP was developed by Texas Instruments and also sold independently, allowing it to be used in other systems. Graphics in the 99/4A are generated by a TMS9918A Video Display Processor (VDP), with a variant for PAL territories. Several sets of registers can be selected by changing the internal workspace pointer register. Sixteen general-purpose mathematical and logic registers are stored in the 256 bytes of scratchpad memory. Only the program counter, status register, and workspace pointer registers are on the chip. Although a full 16-bit processor, only the system ROM and 256 bytes of scratchpad RAM are available on the 16-bit bus. The TMS9900 is a single-chip implementation of TI's TI-990 minicomputers. Later versions of the 99/4A, identified by (C)1983 TEXAS INSTRUMENTS V2.2 on the title page, lack the ability to use unlicensed ROM cartridges, locking out third-party manufacturers such as Atarisoft.īoth TI-99/4 models use the 16-bit TMS9900 CPU running at 3 MHz. Peripherals include a 5¼' floppy disk drive and controller, an RS-232 card with two serial ports and one parallel port, a P-code card for Pascal support, a thermal printer, a 300-baud acoustic coupler, a tape drive using standard audio cassettes as media, and a 32 KB memory expansion card. Unlike most BASICs, only one statement is allowed per source line. It's an ANSI-compliant BASIC interpreter, based on Dartmouth BASIC, with additions for graphics, sound, and file system access. The system displays lowercase letters as smaller capitals, rather than separate glyphs. An external power supply varies with the country of sale, and an RF modulator allows the use of a television as a monitor.

The TI-99/4A is a self-contained console with the CPU, motherboard, ROM cartridge slot, and full-travel keyboard in the same case. Even with the increased user base created by the heavy discounts, after a US$330 million loss in the third quarter of 1983, Texas Instruments announced the discontinuation of the TI-99/4A in October 1983 and stopped production in March 1984. By 1983, the 99/4A was selling for under US$100, at a loss. Commodore's CEO Jack Tramiel had once been offended by TI's predatory pricing during the mid-1970s, and retaliated with a price war by repeatedly lowering the price of the VIC-20 and forcing TI to do the same. The TI-99/4A was launched about the same time as the Commodore VIC-20. TI released developer information and tools, but the insistence on remaining sole publisher continued to starve the platform of software. TI supported the 4A with a peripherals, including a speech synthesizer and a 'Peripheral Expansion System' box to contain hardware add-ons. At half the price of the original model, sales picked up significantly. It includes a simplified internal design, a full-travel keyboard, improved graphics, and a unique expansion system. The TI-99/4A was released in June 1981 to address some of these issues. The calculator-style keyboard is a weak point, and the system suffered a lack of commercial software because of TI's requirement for ROM cartridge and only providing developer information to select third parties. TI's own video display controller allows color graphics and among the best sprite support of its era. Based on the Texas Instruments TMS9900 microprocessor originally used in minicomputers, it was the first 16-bit home computer.

The TI-99/4 is a home computer released in late 1979 by Texas Instruments. Home computer by Texas Instruments Texas Instruments TI-99/4A

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