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Theory of Operation
1780R-Series Service Manual
3–61
Enable (/ANDBE) controls communication with the circuitry on the Annex
circuit board.
Address Latch. U101 is a tri-state device conducting A-to-B only because G is
tied low and the DIR tied high. It outputs three External Addresses
(EA0-EA1-EA2) used as controls on the Waveform, Oscillator, Z-Axis, and
Filter circuit boards. In addition, it outputs the External Read (/ERD), Write
(/EWR), and Restore (/ERST0) used to time the Keyboard/Display circuits on
the Annex circuit board.