| 摘要 |
1297394 Shifting circuit BURROUGHS CORP 17 Dec 1969 [8 Jan 1969] 61537/69 Heading G4C An electronic shifting network comprises a number of gating levels each consisting of a number of sets (rows) of gates, each gate being represented by a number which indicates the bit position (column) in the previous level from which it received its input. The outputs of the gates in each bit position (column) are connected as inputs to an "OR" gate, the output of which supplies a gate in each set (row) in the next lower level. It can be seen from the drawing that each set (row) of gates in each level produces a right shift indicated by the number to the left of the row by virtue of the way its gates are connected to the outputs of the previous gating level. A control circuit is described which enables selected rows of gates to produce the desired shift, e.g. a shift of 21 being produced by enabling shift rows 16, 4 and 1. The network is arranged to produce right and left shifts left shifts being converted to the equivalent right shift in the control circuit by complementing. Each shift may be an "end-around" shift, i.e. the bits shifted off one end being brought round to the other, or an "end-off" shift where the bits shifted off one end are lost. In the latter case certain gates in a selected row are not enabled, e.g. in the 16 shift row of the first level, the first 16 gates (cross hatched) are not enabled so that bits 48-63 of the input word do not appear in the shifted word. All gates which are crosshatched to the right and left are not enabled for right and left "end-off" shifts respectively. |
