GB1512220A - Method of providing a substitute memory module - Google Patents

Abstract

1512220 Data processing NORTHERN TELECOM Ltd 29 Oct 1975 [12 Nov 1974] 44698/75 Heading G4A A low priority memory module M1 is marked, by setting a spare marker 107 to 1, to be used as a substitute for a higher priority memory module M2 or M3 which develops a fault. In normal operation each called address is fed to a comparator 102, coincidence of the called address with the memory module address in a store 101 enabling store 21 via gates 103 and 111. If a fault develops in a memory module the address of the faulty memory module is entered in an address register 400 and a 1 is output on a bus 300 which disables AND gate 103 in the marked memory module M1 to prevent it responding to its own address. Data identical to that in the faulty memory module is then loaded, for example from a standby magnetic tape unit, into the store 21 of the marked memory module M1. Each called address is fed to a comparator 500 and on coincidence with the faulty memory module address in address register 400a 1 is output on line 200 to enable store 21 in the marked memory module M1 via gates 110 and 111. The memory modules M1-M3 may form part of the control unit of a multi-line, multistation telephone exchange system.