vector control for the Junior Computer

74 vector control for the Junior ENA d 2 E RAM 0 LE ROM 0 Nigel Humphreys Computer 1LS30 iet - ivo = wc - ,4LS00 N6 ... N8 = IC3 = 74LS86 The circuit described in this article makes it possible to read out the necessary vector data from the standard EPROM of the Junior Computer, without having to give up a considerable part of the address range and/or requiring an additional ROM. The vectors for NMI, RES and 1 RQ are located at the addresses FFFA ... FFFF. The complete memory range of F000... FFFF would be "sacrificed" for 6 bytes if the above vectors were to be read out of the standard EPROM according to the method described in the Junior Computer Book 3. This means a loss of 4 K memory location. With the solution described here, only 16 bytes are reserved to read out these 6 bytes. Obviously, this circuit is only needed if the constructor 5V ® î T 1a la IC1 IC2 7 7 12 83526 1a IC3 7 13 but an ENABLE ROM signal is sent to the standard EPROM of the Junior Computer. The complete...