RCA 301 Programmer's Reference Manual
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5 Read Simultaneous (RFS)General DescriptionThis instruction reads a series of consecutive characters from a magnetic card on a 3488 unit starting at the blockpreviously selected by the Select instruction. The instruction terminates and the transfer of information ends when thespecified HSM area is filled or the last character of block 255 is read, whichever occurs first. This instruction isperformed in the Simultaneous Mode.FormatOperation — 5N — Specifies device number.(60)8 to (63)8 on Model 380-14 channel.(64) 8 to (67) 8 on Model 380-24 channel.A Address — Address of the HSM location that is to receive the first character of the block previously specified bya Select instruction. Must be an even address.B Address — Address of the HSM location that is to receive the next to last character read. Must be an even address.Outline of OperationIf all conditions are acceptable, the read begins when the 3488 unit indicates that the beginning of the selectedblock has been reached. The Block Address Register in the 3488 unit counts up with each block read.If A-B Equality is not obtained by the completion of the read of the last block of the band, the block addressis incremented by one and, if required, the heads are repositioned. When this occurs, the channel will not terminate the instruction. The read continues when the first character of the next block is in position to be read.Reading of a complete block is not mandatory; A-B Equality can be used to terminate the read whenever desired.Reads will automatically terminate after block 255.When A-B Equality is reached, data transfer and the Read instruction are terminated, the Simultaneous Modeand the channel are freed; however, the 3488 unit remains busy with the read until the interblock gap is reached.When the interblock gap is reached, the Test for Read or Write busy indicator is reset and a Block Preselect, if any,is executed.Whether the card stays on or leaves the capstan after a read is terminated is under control of the Select instruction. If a single bit within a character is missed during a read, the hardware automatically replaces the missing bit, setsthe single bit corrected indicator, and continues reading. If more than one bit within a character is missed, (57)sreplaces the bad parity character in core memory, the parity error indicator is set and the read operation continues;any subsequent bad parity characters are also replaced by (57)8's. When a read is terminated with the parity errorindicator set, the card remains on the capstan even though the select instruction specified its removal. Informationfollowing the first error character within the same block is not reliable.When a read is illogically issued following either an unconditional card removal, or a conditional card removal(Select option A22° = 0) the instruction remains staticized until a card reaches the capstan or the unit goes inoperable.The channel allows only one read (or write) operation at a time. Two channels allow two reads (or writes orread and write) simultaneously.If a Read instruction is issued that misses the beginning of its specified block the operation is automatically heldoff until the block approaches on the next revolution.Final Register Contents(S)f = Address of HSM location one to the right of the last character transferred to memory.(T), = (B),XV-6 |
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