MSM80C154S/83C154S/85C154HVS503.2.2 Reset Schmitt trigger circuitThe Schmitt trigger circuit connected to the RESET pin shown in the MSM80C154S/ MSM-83C154S reset circuit block diagram in Figure 3-4 operates in the following way when the VCCpower supply voltage is +5V.If the voltage of the reset signal applied to the RESET pin exceeds 3V when the level of thatsignal is changed from “0” to “1”, the Schmitt trigger output level is changed from “0” to “1”,and the reset signal is set in the CPU reset control circuit, resulting in the reset operation beingstarted by the CPU.The CPU reset state is released when the “1” level on the RESET pin is changed to “0”. Aninput signal level below 1.5V is regarded as “0” level, and the Schmitt trigger output level ischanged from “1” to “0”. When the reset signal is changed to “0” level, the CPU reset controlcircuit is ready for reset release. The Schmitt trigger circuit operation time chart for changesin the reset input voltage is outlined in Figure 3-9.VIH = 3.0[V]••5 [V]0 [V]5 [V]0 [V]5 [V]0 [V]V CCRESETSchmitt trigger gate outputVIL = 1.5[V]••CPU resetcontrol inputVTH = 1.5[V]••Figure 3-9 Reset Schmitt trigger gate detector time chart
