EDDA 3 - Operational Safety

Parent Category: Articles Category: EDDA 3 - An Early Transistorized Process Computer Written by Administrator

Because EDDA 3 was deployed in industrial environments and the computer controlled expensive, complex production lines, it had to be very reliable. This was achieved by the following measures:

1) It is checked after each program instruction if the result really has been written to the core memory or to the peripheral register ("Control Clock"). In case of an error the current instruction is repeated several times. This maintains the integrity of the core memory and a simple handshake can be done with the peripherals. If the instruction repetition lasts too long, a jump is done to program address 01; this coraresponds to a "bus timeout exception" in modern CPUs. The maximum repetition time in case of an error can be set externally to a range of 5 milliseconds up to 2 seconds.

2) The manual contains detailed procedures for troubleshooting, from flowcharts for fault localization to measuring and soldering instructions:

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3) Lamp strips were placed on different expansion cards to visualize internal voltage levels.

4) Two EDDAs could be linked to a fail-safe network: If one EDDA failed, it was automatically switched to a stand-by device.

The EDDA was checked by the PTB (the  German metrology institute) and approved for "eichamtlichen Verkehr". This means "it is officially certified that it either calculates correctly or it emits a fault signal”.