0.2V of LOW level are satisfactory. However, HIGH level output of 4V will exceed maximum VDD+0.3 of the input permission voltage of the device currently operated by 3.3V, 3.6V [ i.e., ].

On the other hand, it is inserted in the direction to which the diode for protection of static electricity destruction flows toward a power supply from an input terminal for the input terminal of almost all CMOS devices.

Although excessive current may flow and break to this diode, a latch rise has the higher possibility than it.

In the case of CMOS, the bipolar transistor which is not meant in case MOS transistor is built with a diffusion process will also be made as a by-product. Although this is called parasitism transistor, the parasitism transistor of both PNP and NPN will be made. Furthermore, since this transistor becomes complicated circuit composition to a bad thing, a part will become thyristor structure.

Once a thyristor is turned on [ it ], it has the character in which current continues flowing. It is called latch rise that the thyristor made with the parasitism transistor is turned on [ it ].

If a latch rise happens, between the power supply grounds inside a device will short-circuit, large current will flow, and it will be destroyed at an instant.

In order to turn on [ it ] a thyristor, a certain amount of current is required. That is, in order for HFE of the constituted transistor to become large, a certain amount of current is required. Although the latch rise is making to design a device and to happen, a device is made and it is dependent on condition, so that it may become as large as possible about the value.

Therefore, if supply capability in case the device which starts passing current is H level is smaller than the latch rise current of the device which receives current, a latch rise will not happen.

However, since it is serious to verify this, the voltage by the side of supply is lowered, and current is made not to flow. Since there is voltage descent of a 0.5V about if a diode is inserted in a power supply, the output voltage of 74AS04 can be estimated at 3.5V.Although this value is larger than 3.3V, since a bipolar transistor cannot be changed into an activity state, it is safe.

In addition, it may assemble now, may operate and the thing circuit without a diode is satisfactory for those satisfactory. It is because the supply current of HIGH level of 74ASs04 is considered to have been less than the amount of -proof [ latch rise ] of IC.