JAS 39 Gripen - an overview of the internal network

JAS 39 Gripen - an overview: The internal network

Gripen uses MIL-STD 1553B databuses, all of which most of the time are utilized 40-60% of their capacity. At first there were three of them, now they're five, operating at 1MB/s. The computer system Ericsson SDS 80 uses D96/MACS processors (since 2000 -- initially D80 processors, upgraded to D80E in 1994, were used) which are programmed with Pascal-D80, which has advanced real time functions and Ada. CPU load can be as much as 95% without any problems.

The MACS has three 266 MHz PowerPC processors working in parallell, 160 MB disk (extensible to 320 MB), 32 MB PROM and 64 MB RAM. Mass 13.5 kg.
The CPUs and buses can't be overloaded unless there's a hardware error, and if this happens the system reverts by graceful degradation to a more conservative, less capable, mode in steps. It can revert to a very basic mode.

All computations are performed in pipelined runbursts, which are governed by a central 60Hz clock, which is the basic frequency, although some processes are run 120 to 240 times per second and less demanding ones can be run 15, 8, 4 or 1 times per second and some in the background. The FCS executes processes for all runburst frequencies and in the background continously.

TCP/IP is used, but only for the Data Transfer Units. One is for the pilot for use with mission planning and debriefing. The other is for the ground crew and records operational data and status of the aircraft and can also be used to reprogram the aircraft's software. Mission planning data can also be uplinked from the ground while in the air.

Databus overview

There are five duplicated and separated for redundancy databuses with different tasks. One is for flying the aircraft itself, one is for the graphics processors, one for targeting and sensors, one for communications and one manages weapons and the HMS.

(Note: I wrote this and made this drawing in 2000. But it can still be of interest.)

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