Texas Instruments HX-2000 Wafertape Digital Tape Drive Prototype

Texas Instruments designed in 1982 with the HEX-BUS a very innovative interface to connect intelligent peripherals like printers, modems or even a video interface to its new Compact Computer System CC-40 and planned to use it with the never released TI-99/8 home computer.

The physical interface of the HEX-BUS is a rather simple 8-pin connector and with peripherals having always two HEX_BUS ports, multiple peripherals can be connected in a daisy-chain mode. The Hardware of the HEX-BUS uses four Data-Signals [D0, D1, D2, D3], two Handshake-Signals [HSK], [BAV] and a common ground signal [GND]. The remaining line was reserved for future use and labeled [FUT]. With the drivers being "open collector", the interface allows bi-directional data communication, each Byte is transmitted in two 4-bit words in a Master/Slave protocol. Texas Instruments published not only the specifications of the HEX-BUS and the software requirements for peripherals, but even offered two different Intelligent Peripheral Bus Controllers (IBC), realized as ASICs (Application Specification Integrated Circuits):

Texas Instruments dropped out of the home computer market in March 1984 - after selling more than 2.5 million of the famous TI-99/4A - and production of the CC-40 was ceased immediately after. Consequently was the development of the HEX-BUS terminated and only a few of the already announced HEX-BUS peripherals were manufactured in significant quantities. Interesting fact to know: The TI-74 BASICALC and TI-95 PROCALC computers introduced in 1985 as successor of the CC-40 use a 10-pin Dock-Bus which is compatible to the HEX-BUS and added three signals: [RESET] and System Power Distribution In [PI] and Out [PO] to power peripherals from the computer or the computer from peripherals.

Texas Instruments announced or released during the short live of the Compact Computer 40 eight different products like printers, plotters and even a serial interface using the HEX-BUS Interface. Additional peripheral devices were planned or released from Third Party vendors but are not listed as of now in our overview:

The HX-2000 Wafertape Digital Tape Drive uses a small, endless loop, magnetic tape called a Wafertape. The Wafertapes vary in length from 5 to 75 feet (1.5 to 22.5 m). The tape speed is about 8 inches per second (0.2 m/s) and the motor runs only during wafer access. Data density amounts to 1.5k Bytes per foot. However, the capacity of a wafer is reduced significantly by a file directory, synchronization patterns preceding data records and motor start/stop time considerations. Thus the maximum access time and the amount of data storage can be traded off by choosing the Wafertapes. Up to 8 HX-2000 may be connected to the HEX-BUS, each unit must have a unique device code selected by two switches and a jumper inside the device. Device codes 1 through 8 in the Intelligent Peripheral Bus specifications have been allotted for Digital Tape Drives.

Texas Instruments announced in 1983 not only the HX-2000 but fourteen Wafertape cartridges with preprogrammed application packages with a Manufacturer Suggested Retail Price (MSRP) of $19.95, each:

Dismantling this battery operated HX-2000 Engineering Prototype manufactured in September 1983 by Texas Instruments in their Abilene, Texas facility, reveals a design with two printed circuit boards (PCBs) connected with a flexible jumper cable.

One PCB of the HX-2000 holds the electronics of the Exatron Stringy Floppy drive, while the second PCB includes the connectors to the outside world, the power supply and illustrates a single-chip microcontroller design with just two main building blocks:

CPU (Central processing Unit): The Texas Instruments TMC70C20 microcontroller is a member of the TMS7000 family manufactured in CMOS technology. The original design of the TMS7000 series was introduced in 1981 as an 8-bit extension of the TMS1000 Family to compete with already well established Intel i8051, Motorola M6801, and Zilog Z8 products. The first chips sported 128 bytes of on-chip RAM (Random Access Memory) and either 2k Bytes or 4k Bytes of ROM (Read Only Memory). The featured HX-2000 Engineering Prototype sports a TMX70C20 with ROM-Code L11001 a very early prototype of the TMC70C20, equipped with 2k Bytes of ROM. Read more about TI Standard Symbolization used in the Eighties with ICs manufactured in a metal–oxide–semiconductor (MOS) process. Interesting to observe that the microcontroller of the HX-2000 Wafertape displays ROM-Code L11001, while the Compact Computer System CC-40 sports ROM-Code C11002.

IBC (Intelligent Peripheral Bus Controllers): The IBC ASIC (Application Specific Integrated Circuit) with TI part number 1059211 was manufactured by LSI Logic in their then state-of-the-art 2 um CMOS process and is marked accordingly with L1A0037 (L1A references to the ASIC family and 0037 is # of the design within the ASIC family).

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, October 27, 2019. No reprints without written permission.