Type Lowercase Letters Ti-84
Type Lowercase Letters Ti-84 – “Texas Instruments Home Computer” redirects here. For a computer called Texas Instrumts PC, see Texas Instrumts Professional Computer.
Based on the Texas Instrumts TMS9900 microprocessor originally used in minicomputers, the TI-99/4 was the first 16-bit home computer,
Type Lowercase Letters Ti-84
The associated video display controller provided some of the best color graphics and sprite support available at the time.
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The TI-99/4’s calculator-style keyboard was considered a weakness, and TI’s reliance on ROM boxes and their practice of limiting developer information to select third parties resulted in a lack of software for the system. Released in June 1981, the TI-99/4A was designed to address some of these issues, featuring a simplified internal design, full-travel keyboard, improved graphics, and a unique expansion system. At half the price of the original model, sales have picked up significantly, and TI supports 4A peripherals, including speech synthesizers and “peripheral expansion system” boxes that include hardware add-ons. TI released developer information and tools, but insisted on keeping a sole publisher and continued to starve the software platform.
The TI-99/4A was introduced in the US in 1981, a few months after the Commodore VIC-20. Commodore CEO Jack Tramiel was disgusted with TI’s predatory pricing in 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. By 1983, the 99/4A was selling for under $100 and at a loss. Texas Instruments loses $330 million in third quarter of 1983 as user base created by deep discounts increases
The TI-99/4 was intended to be installed in the middle of a planned family of TI-99 computers, none of which were ultimately released, but prototypes and documentation were rediscovered after the TI-99/4A was discontinued.
The TI-99/4A is a standalone console with the motherboard, ROM slot and full travel keyboard in the same chassis. The power supply is external. RF modulators allow the TV to be used as a monitor. Lowercase letters are displayed as small caps instead of separate glyphs. TI BASIC is an ANSI-compliant BASIC interpreter based on Dartmouth BASIC, which is built-in and includes support for graphics, sound, and file system access. Later versions of 99/4A, identified as
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Peripherals include a 5¼” floppy disk drive and controller, an RS-232 card with two serial ports and one parallel port, a Pascal-enabled P-code card, a thermal printer, a 300 baud acoustic coupler, A cassette using a standard tape drive as media and a 32 KB memory expansion card.
Both TI-99/4 models use a 16-bit TMS9900 CPU running at 3 MHz. The TMS9900 is a single-chip implementation of TI’s TI-990 minicomputer. Although a full 16-bit processor, only system ROM and 256 bytes of scratchpad RAM are available on the 16-bit bus.
A computer requires not only a CPU, but also many I/O, memory, and other support chips for the system. TI is a major supplier of such systems, but most of them are 8-bit designs. To build a complete 16-bit system, the company had to redesign these support systems in 16-bit form. Instead, for the computer project, they decided to use existing 8-bit devices for most of the system. Only a small portion of the system was 16-bit, the rest used a second 8-bit computer bus.
One of the key features of the TMS9900 comes from the minicomputer design from which it was created, which contains sets of processor registers. Registers are used to store information that a particular program is actively processing, rather than main memory, which stores more data but is slower to access. In a minicomputer environment, the system typically runs a time-sharing or multitasking operating system, or is used for real-time computing, both of which benefit from being able to switch quickly between programs. To do this, the TMS9900 stores sets of registers in main memory and can switch between sets of 6 16-bit registers by changing a single workspace pointer register, enabling very fast context switching.
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Because the performance of registers is critical to the overall performance of the machine, the new design places 256 bytes of random access memory (RAM) on a 16-bit bus to store up to eight sets of registers. This area of RAM is called “scratchpad memory”. Since the processor’s instructions are also 16-bit, the 8 KB of internal system read-only memory (ROM) is also 16-bit.
The 8-bit side of the system includes most of the RAM and almost all supporting chips, especially the Video Display Controller (VDP). All accesses to the VDP system are performed 8 bits at a time.
The system’s RAM is managed by VDP, which provides access to the CPU only when the CPU is not using memory. This means that the user program and data must be read in two machine cycles, reducing the speed in half. According to IEEE Spectrum, this negates the performance benefits of 16-bit processors.
Graphics in the 99/4A are generated by the TMS9918A Video Display Processor (VDP) and have variants for PAL regions. VDP is developed by Texas Instruments and sold independently and can be used with other systems. It is used as the video processor for the ColecoVision and SG-1000 consoles, and earlier models were part of the MSX computer standard.
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The TMS9918A supports character and bitmap based display modes as well as hardware sprites. There are 32 monochrome sprites in total, but only a maximum of 4 can be displayed per scanline. Each sprite is 8×8 or 16×16 pixels and can be scaled 2x to 16×16 or 32×32.
16 KB of RAM is provided for the video display processor. VDP RAM is the largest block of writable memory in the unextended TI-99/4A architecture and is used to store disk I/O buffers and TI BASIC user programs. Access to this memory must use VDP as an intermediary.
All TI-99 models have device drivers built into the hardware’s ROM. Once the new peripheral is connected, it can be used immediately by any software that wants to use it. All device access uses a file-based generic I/O mechanism, allowing new devices to be added without software updates. The system supports four RS-232 ports and two parallel printer ports.
The computer supports two tape drives through dedicated ports, using a custom data format. Composite video and audio are output through another port on NTSC-based machines and combined through an external RF modulator for use with a TV. PAL-based machines output a more complex YUV signal that is also externally modulated to UHF.
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Two digital joysticks can be connected via a DE-9 port. It’s the same as the Atari joystick port, but it’s not pin compatible. Aftermarket adapters allow the use of Atari-compatible joysticks.
Memory is not suitable for all purposes. For example, an Extded Basic program is limited to 24 KB, leaving the remaining 8 KB available for machine code routines. The Mini Memory plug-in module contains 4 KB of battery-backed RAM that can be used as a persistent RAM disk or to load machine code programs.
The TI-99/4A can be upgraded by adding expansion cards to an eight-slot external chassis, which contains its own linear power supply and a full-height 5¼” floppy disk bay.
Comes in a silver plastic case, but is made of steel, this is TI labeled as a Peripheral Expansion System, but is often referred to as a Peripheral Expansion Box or PEB. Each card has an LED indicator that flashes or flashes when accessed by software. The part of the power supply that powers the card slot is not regulated. Each card has on-board voltage regulators for its own requirements, reducing power consumption for partially loaded PEBs, allowing cards with unusual voltage requirements.
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The PEB carries the analog sound input on the expansion bus, allowing the audio from the speech synthesizer to be routed through the console to the monitor. Audio is also routed to the PEB via a ribbon cable, both allowing the speech synthesizer to be relocated to the PEB and allowing the sound card to provide more functionality than the console’s built-in sound. TI’s official cards do not do this.
In the late 1970s and early 1980s, TI was a pioneer in speech synthesis, as its Texas Instruments LPC speech chips were used in its Speak & Spell toys. The TI-99/4 and 4A can use a plug-in speech synthesizer module. Speech synthesizers are available for free with the purchase of some cartridges and are used by video games such as Alpiner and Parsec. Alpiner’s speech includes both male and female voices and can be sarcastic when players make the wrong move.
The synthesizer uses a variant of linear predictive coding and has a small built-in vocabulary. The original intt was to release small cassettes that inserted directly into synth units to increase the vocabulary of the device. However, the success of software text-to-speech in a Terminal Emulator II box canceled the plan.
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