Calling junior vectors - a useful junior computer modification

Appendix 3 of the Junior Computer Book 3 shows that the system vector data can be called from the standard EPROM with a busboard memory without having to use an extra EPROM. This circuit is an elegant alternative for solution number one. The following modifications must be incorporated. N102 must be replaced by a wire link. Wire links R-S and D-EX have to be mounted on the interface and standard board respectively. Pin 8, which is the output N34 of IC13 on the interface board, has to be bent out, so that the connection to point EX -NO is interrupted. This connection is now made via the open collector outputs of gates N1 and N2. Only eight memory locations have to be "sacrif iced" ($F F F8 . . . $ F F F F), because IC1 has not less than 13 inputs (connected address lines). A3 R. Matyssek A4 AS A6 5V calling junior vectors 5V • see text N1,N2 = 1/3 IC2 = 7417 N3 = IC1 = 74LS133 304 EX = 81(8 a useful junior computer modification (IC13) A7 AS AS A10 All Al2 Al 3 A14 A15 N1 82602 14