Abstract: An improved circuit modification method is provided for wire-wrapped electrical back planes such that changes in the back plane circuitry may be accomplished in areas remote from a production facility where wire-wrap equipment and highly skilled technicians may not be available, such method involving the preparation of a slip-on, post-terminal-compatible printed circuit board at the production facility, delivery of the printed circuit board to the remote area, and the slip-on attachment of the printed circuit board onto the post terminals of the back plane by a repairman who may be unfamiliar with the intricacies of the back plane and its wire-wrapped interconnections, said slip-on printed circuit board being inherently provided with whatever guidance may be required by the repairman in effectuating its installation on the back plane.

Abstract: Relates generally to the production of electrical signals from a keyboard, each key of which is individually operatively associated with a switching device whose activation to electrical conductive condition is controlled by the displacement of the key. These switches are hermetically sealed from the atmosphere and are electrically scanned in succession at relatively high speeds and at a repetitious rate such that several scanning cycles occur during the normal activation of a selected key. The keyboard mechanism also includes a shift register having one more bit position than the number of switch devices and into which a bit is introduced into the "one" position at the instant the scan encounters a closed switch of the keyboard. This bit is then shifted through the register in timed relation to the scan of the remaining key switches and unloaded into the last bit position of the register.