Reset For The Pc 1640

002 COMPUTERS RESET FOR THE PC 1640 The PC1640 is one of Amstrad"s popular and successful series of compact PCs. It has, unfortunately, a serious deficiency: there is no reset control. Luckily, it is not too difficult to fit this control ret- rospectively, since every Pc, and the 1640 is no exception, has a reset circuit. In the 1649, the circuit shown below monitors the level of the supply voltage. This voltage is sampled by potential divider R151-R152-R176-R188. If the supply is too low, the Q105, and consequently the Q104, switches off. Transistor Q106 is also pro- vided with too little bias voltage to conduct. The enable input of the cmos memory, IC134, is linked to the collector of Q105, so that when Q105 is turned off, the memory is disabled. At the same time, the supply to the memory is switched off since Q104 is off. Vcc IC134 0106 2SAIOIS R140 10K CE 04 D104 155132 IC134 RI SO 10K 894007-11 PWROK ELEKTOR ELECTRONICS JULY 1989 SUPPLEMENT Only when the supply voltag...