The IEEE 1394 and I2C Mixed-Signal Driver is one of two application-specific integrated circuits (ASICs) designed to function together as an interface among the following three digital-signal buses:

  • A peripheral component interface (PCI) bus;
  • A high-speed serial data bus that conforms to Institute of Electrical and Electronics Engineers (IEEE) standard 1394, also known as the FireWire standard; and
  • An I2C (inter integrated circuit) bus, which was developed in the early 1980s by Philips Semiconductors for connecting a central processing unit to peripheral integrated-circuit chips in a television receiver.

Among other things that have been emphasized in the development effort are radiation hardness and compactness as required for intended use aboard spacecraft. As result of engineering compromises necessary for radiation hardness, the performance of this set of ASICs is expected to lag somewhat behind that of comparable circuitry previously developed for terrestrial use. Nevertheless, because the capability for communication among the three buses is not afforded by any plug-in circuit cards now commercially available, there could be a terrestrial market for these ASICs for applications in which the tri-bus communication is required.

In the original spacecraft application, the two ASICs would enable communication among multiple computers, scientific instruments, and spacecraft engineering systems via the three buses. The first ASIC, which could be characterized as a digital input/output (DIO) ASIC, would provide a digital interface (a link layer) among the three buses. The second ASIC, denoted the IEEE 1394 and I2C Mixed-Signal Input/Output Driver ASIC (“MSIO ASIC” for short) is the focus of this article. The MSIO ASIC would serve as the physical layer in the overall data-communication architecture.

The MSIO ASIC would implement an analog interface to the IEEE 1394 and I2C bus cables. The MSIO ASIC would be connected, either directly or through an isolation transformer, to the DIO ASIC. The MSIO ASIC would receive digital commands and data from the DIO ASIC and pass these data and commands out through the IEEE 1394 and I2C cables. The MSIO would contain a commercial controller core, custom analog bus cable-driver circuits, two I2C-bus cable-driver cores, and custom glue-logic circuitry. The MSIO ASIC would be a radiation-hardened, galvanically isolated, three-port implementation of the physical-layer functions described in the IEEE 1394a D2.0 draft specification. The MSIO ASIC would also contain two radiation- hardened, galvanically isolated sets of I2C drivers and receivers, independent of the 1394 interface and of each other.

This work was done by Huy Long, Peter Jones, Savio Chau, and Eric Holmberg of Caltech and Ross McTaggert of Digital MediaCom for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at  under the Electronic Components & Systems category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Intellectual Property group
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240

Refer to NPO-30121, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
Document cover
Mixed-Signal Driver ASIC for IEEE1394 and I2C Buses

(reference NPO-30121) is currently available for download from the TSP library.

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