screen-noise killer - for the VDU card with the CMOS Junior

for the VDU card with the CMOS Junior The VDU card published in Elektor number 101, September 1983, sometimes lets noise appear on the screen, such as when a program is being listed. This fault can easily be remedied by means of a few gates in the VDU card that are unused in the Junior Computer/VDU card combination. The trick of the circuit consists of stopping the processor when it at- tempts to write to the video RAM during the display enable time. Only the 65CO2 can be stopped during writing so this circuit operates ex- clusively with Junior Computers equipped with the CMOS Processor. This procedure causes a slight delay in the output of a program but this is hardly noticeable in practice. In order to carry out the modification the following IC pins on the VDU card are bent out to the side so that they are no longer in the IC sockets: IC2 pins 7, 9, 11 and 13 IC4 pins 1, 8, 9 and 10 IC7 pins 1, 8, 9, 10, 11, 12, and 13 IC8 pin 8 IC17 pin 1. These pins are then connected togethe...