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139 Appendix D - ZX-44 Series Hardware Reference The ZX-44 is the 44-pin TQFP package version of the Atmel AVR ATmega32 microcontroller that has been programmed with the ZX control firmware. Similarly, the ZX-44a is the 44-pin TQFP package version of the Atmel AVR ATmega644 microcontroller. They offer the same capabilities as the ZX-24 plus access to 7 additional I/O pins. In order to use the ZX-44/ZX-44a you must add several additional components as described below. In each of the diagrams presented below, only a portion of the ZX pins is shown. Those that are not germane to the circuit being discussed are omitted for clarity. D.1 ZX-44 Series Specifications The electrical specifications of the ZX-44 are exactly those of the ATmega32. Likewise, the electrical specifications of the ZX-44a are those of the ATmega644. Rather than reproducing them here the reader is directed to the datasheet published by Atmel. It can be obtained from the Atmel website | http://www.atmel.com or from the ZBasic website |http://www.zbasic.net. D.2 ZX-44 Series Required External Components Power Source The ZX-44 series devices need a regulated voltage source capable of providing at least 200mA of current. The voltage typically used is 5 volts but the ZX-44 series devices will operate between 4.5 volts and 5.5 volts. A recommended circuit is shown below. A suitable heatsink will probably be required in most cases to keep the regulator IC below its maximum operating temperature. Consult the regulator datasheet for more information. ZX-44 Series Power Source If you do not plan to use the Analog-to-Digital converter channels you can eliminate the inductor and the two capacitors on the right side of the diagram. In this case, pin 27 would be connected directly to the power source (same as pin 5, etc.) and pin 29 can be left open. Although not shown on this diagram, the ground pins of the ZX-44 (pins 6, 18, 28 and 39) must be connected to the common ground of the system. Clock Source The ZX-44 series devices require 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 7 and 8 along with the necessary capacitors. The recommended crystal to use is ECS-147.4-20-4 (Digi-Key #X175-ND). An alternate crystal in a slightly larger package is ECS-147.4-20-1 (Digi-Key #X142-ND). The capacitor value to use depends