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148 meet the RS-232 standard. Even so, most serial receivers are able to properly interpret the output signal. Note that if the inverters used have protection diodes on their inputs the external diodes shown are not necessary. The second alternate serial interface is shown in the diagram below. This circuit produces a serial output signal that meets the RS-232 standard by using the negative voltage on the receive line to provide a reference for the output level. Although the parts count is higher, the circuit uses inexpensive and non- critical components. Alternate Serial Interface Circuit #2 Reset Circuit You may also want to incorporate a reset button in your circuitry. If so, a normally open, momentary contact switch may be connected directly between pin 20 of the ZX and ground. If other circuitry in your application also needs the reset signal, you may want to isolate that circuitry from the ATN resets using a buffer gate or a diode. A suggested diode isolation circuit for the reset line is shown below. Reset Signal Isolation