Texas Instruments HX-3000/P RS-232 Interface with Parallel Interface

Date of introduction:  1983 Display technology:  
New price:  $124.95 (MSRP 1983) Display size:  
Size:  5.8" x 4.6" x 1.4"
 148 x 118 x 36 mm3
Weight:  9.3 ounces, 263 grams Serial No:  0000205
Batteries:   Date of manufacture:  wk 21 year 1983
AC-Adapter:  AC9203 Origin of manufacture:  USA (ATA)
Precision:   Integrated circuits:  CPU: TMC70C20 C14018
 ASIC: LSI Logic L1A0037
 ACIA: SY6551
Memories:   HEX-BUS Device ID:  50-53
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 9.3 MByte)

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):

TI # 1052911, LSI Logic ASIC L1A0037, 22 pin Package
TP0370, new version, 28 pin package

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:


Name / Description

MSRP (1983)


HX-1000 Printer / Plotter 4 colors $199.95 Series
HX-1010 Printer 80 (Thermal ribbon) $249.95 Series
HX-1100 Video Interface $99.95 Prototype
HX-2000 Wafertape Digital Tape Drive $139.95 Prototype
HX-3000 RS-232 Interface $99.95 Series
HX-3000/P RS-232 + Parallel Interface $124.95 Series
HX-3100 Data Modem $99.95 Series
HX-5102 Disk Drive/Controller t.b.d. Prototype

The HX-3000 RS-232 allows direct connection of the Texas Instruments Compact Computers to serial-input printers and modems. With the addition of an optional cable, the interface HX-3000/P can connect to a parallel-input printer.

Dismantling this HX-3000/P RS-232 Interface with Parallel Interface manufactured in May 1983 by Texas Instruments in their Abilene, Texas facility, reveals a very clean design with just one printed circuit board (PCB).

The PCB of the HX-3000/P holds all the connectors to the outside world, the optional cable for the Parallel Interface, the power supply and illustrates a single-chip microcontroller design with three 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-3100 sports a TMC70C20 with ROM-Code C14018, 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.

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).

ACIA (Asynchronous Communication Interface Adapter): Synertek, a subsidiary of Honeywell, introduced already in 1981 with the SY6551 a very popular and truly versatile device for the 6500/6800 CPU family. The SY6551 ACIA includes an on-chip programmable baud rate generator, with a crystal being the only external component required. Fifteen programmable baud rates between 50 and 19,200 baud can be derived from a 1.8432 MHz crystal and an external clock input allow non-standard baud rates up to 125,000 baud. An 8-bit bi-directional data bus allows direct communication with most microprocessord or microcontrollers.

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