MSM80C154S/83C154S/85C154HVS

3.2.2 Reset Schmitt trigger circuit

The 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 VCC power supply voltage is +5V.

If the voltage of the reset signal applied to the RESET pin exceeds 3V when the level of that signal 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 being started by the CPU.

The CPU reset state is released when the “1” level on the RESET pin is changed to “0”. An input signal level below 1.5V is regarded as “0” level, and the Schmitt trigger output level is changed from “1” to “0”. When the reset signal is changed to “0” level, the CPU reset control circuit is ready for reset release. The Schmitt trigger circuit operation time chart for changes

in the reset input voltage is outlined in Figure 3-9.

5 [V]

VCC

0 [V]

5 [V]

RESET

0 [V]

5 [V]

Schmitt trigger gate output

0 [V]

3.0[V]

1.5[V]

VIH =

VIL =

 

1.5[V]

 

 

VTH =

 

CPU reset

control input

Figure 3-9 Reset Schmitt trigger gate detector time chart

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Sonic Alert msm83c154s, msm80154s, msm85c154hvs user manual MSM80C154S/83C154S/85C154HVS Reset Schmitt trigger circuit