External Bus (U-BUS)The U-BUS consists of two ribbon cables termed A and B respectively, ended with D-SUB connectors that plug from unit to unit in Daisy-Chain topology. Signals in the U-BUS are the following (NOTE: The actual pin-out has not been defined yet):
CABLE A (D-SUB 25)
- - - - - - - - - -
ADDR LOWER : A0-15
ADDR UPPER : A16-23
CABLE B (D-SUB 37)
- - - - - - - - - -
DATA : D0-15
CONTROL : MRD, MWR, MWT, IRQ, IAK, BSY, SRT
RESERVED : Future use (13)
Power (+5V) is not present in the U-BUS since units are self-powered.
Control Signals in the U-BUS
MDR: Memory Read
MWR: Memory Write
MWT: Wait (for synchronization with slow devices)
IRQ: Interrupt Request
IAK: Interrupt Acknowledge
BSY: Bus busy (not in 3rd. state)
SRT: System Reset
Note: Peripherals are memory mapped.
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