RCA 301 Programmer's Reference Manual
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D Band Select Normal (BSN)General DescriptionThis instruction initiates a search of a designated Data Record File for the record containing a specified band,places the record on the turntable and advances the read/write arm to the "ready" position. Once this instructionis initiated (staticizing and establishing a control counter), the data record and band are selected independent ofcomputer operation.A Band Select Normal instruction must be issued prior to a Block Read (or Write) Record Normal (or Simultaneous) instruction (BRN, BRS, BWN, BWS). These instructions may be used to address one of two Data RecordFiles controlled through a Data Record File Control.FormatOperation —DN — Selects the Data Record File Unit and Band as indicated below:1 st File 2nd File Effect0 & The record on the turntable, if any, will be returned to the cage. Thedesired record is then placed on the turntable and the indicated bandselected.1 A The band selected is one of the two on the upside of the record on theturntable. If the B address is even, the first band will be selected; if odd,the second band will be selected.A Address — Must be zeros (0000).B Address — B0 must be zero (0); B1; B2, B3 designate band (000 to 511).Outline of OperationBand addresses are numbered from 000 through 511 and are specified by the last three digits of the B address.The contents of the N Register designate the proper Data Record File and specify whether the record on the turntable, if any, is to be returned to the cage or not.Final Register Contents(A)f = (A),(B)t = (B),TimingA. Computer time to initiate selection (staticizing and establishing address counter) in microseconds: 21 (B,)+ 14 (B2) + 42.B. Select data record from storage wheel:Note. Since the 128 position data record storage wheel rotates in either direction, the maximum data recordposition from the selection point is 64.XI-3 |
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