External Bus (E-BUS)All units connect to the External Bus (E-BUS) which is made of two multi-pair cables (termed A and B) ended with D-SUB 25 pins connectors at both edges. A and B cables interconnect units in daisy chain topology.
These are the signals present in each cable. The actual pinout has not been defined yet.
CONNECTOR A
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A00-A19 Address lines
GND Signal Ground
CONNECTOR B
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D0-D15 Data path
IRQT Interrupt Request
IACK Interrupt Acknowledge
DMAR Direct Access Memory Request
DMAK Direct Access Memory Acknowledge
BBSY Bus busy
DTWR Data Write
DTKE Data Take
GND Signal Ground
Power lines are not provided in the bus so units are required to be self-powered.
Signals DMAR and DMAK are similar to IRQT and IACK but they work with Data Access Memory (DMA) rather than interrupt.
Signal DWRT determines whether the bus cycle if for reading or writing (from the Master viewpoint). It is active for write cycles.
Signal DTKE will usually be connected to Output Enable pins (OE) of three-state chips. Actual data transfer occurs when this line is activated.
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