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ZBasic Language Reference 194 ZX Microcontroller Family Clock Source The ZX-32a4n device requires a clock source running at 14.7456MHz. The easiest way to provide this clock source is to connect a crystal of that frequency to pins 36 and 37 along with the necessary capacitors. Some recommended crystals are shown in the table below. Recommended Crystals Package Crystal HC-49/US ECS-147.4-20-4X (Digi-Key #X1102-ND) HC-49/U ECS-147.4-20-1X (Digi-Key #X1032-ND) Cylinder ECS-147.4-18-9X (Digi-Key #XC-1382-ND) ZX-32a4 Clock Source If you already have a clock source at the required frequency you can feed that signal directly to pin 37. In this case there would be no connection to pin 36. Serial Interface The ZX-32a4 device requires a serial interface for downloading code into Program Memory and for your program’s use via Com1. The recommended serial interface circuitry is shown below. This circuit has two sub components. The MAX3232E chip functions as an RS-232 level converter that translates the 0- 3.3 volt signals of the ZX-32a4 to the standard RS-232 voltage levels. The second component is the ATN circuitry that is used to signal the ZX-32a4 to go into download mode. The latter circuitry is that portion connected between pin 4 of the DB-9 serial connector and pin 35 of the ZX-32a4. You may want to include a jumper in the ATN circuitry so that it can be disconnected when downloads are not required. With the ATN circuitry connected, the ZX-32a4 will receive a reset pulse on every positive transition of pin 4 (DTR) of the serial connector. If alternate component values are chosen you must ensure that the ZX-32a4 receives a reset pulse of at least 2uS on every positive transition of the DTR signal on pin 4 of the serial connector. One advantage to using this recommended circuit is that the MAX3232E chip includes a DC-DC converter that produces nominally +/- 10V from a 3.3 volt source. This is particularly useful if your application requires one or more of these voltages. For example, some LCD devices require a low- current negative supply for their backlight circuitry. The positive voltage is available on pin 2 of the MAX3232E while the negative voltage is available on pin 6. Consult the datasheet for the MAX3232E device for information on the current capacity of these supplies. The PDI_DATA pin of the ZX-32a4 (pin 34) is used for factory programming and should be left unconnected.