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ZBasic Language Reference 162 ZX Microcontroller Family Pin 22, Reset You may apply an active low signal to this pin to reset the processor. Note, however, that the on-board reset circuitry will also pull this line low via an open collector output each time the ATN input makes a positive transition (notably during downloading). If you don’t want your external circuitry to receive this reset signal, you must isolate the on-board reset from external devices using a diode, a transistor or an open collector gate. An example circuit is shown in Section C.1. Pin 23, Ground This pin, common with pin 4, serves as the reference for the power supply and all I/O pins. Pin 24, Unregulated Voltage In To use the on-board regulator, you may supply an unregulated (but filtered) voltage source from 7 to 20 volts DC to this pin. The power supply must be capable of supplying at least 150mA. See the description of pin 21 for more information about the on-board regulator and the limitations of using it. It is important to note that the maximum input voltage must be derated above an ambient temperature of 45°C according to the formula V in <= 5 + (125 – T amb ) / 5.2. For example, with an ambient temperature of 75°C the input voltage must be kept below 14.6V. For operating in high ambient temperatures it is recommended to use an external regulator with an appropriate heatsink. Additional Notes: Each of the I/O pins (5-20, 25-27) can source 20mA or sink 40mA (at Vcc=5V). However, the total source current and the total sink current for all pins may not exceed 200mA. This is further limited by the capacity of the on-board regulator if it is being used. At Vcc=3V, the maximum source and sink currents are one-half of the 5V rating. All of the I/O pins (5-20, 25-27) have protection diodes built in. If the signals that you connect to these pins go above V+ or below ground, you must include a current limiting resistor to keep the pin current below 20mA. C.2.2 Expansion Pins The table below summarizes the functions of the ZX-24 series expansion pins. These “pins” are actually holes on the circuit board that require a soldered or mechanical clip connection to use. A detailed description of each pin is given following the table. Expansion Pins Pin ATmega ATxmega 25 Port D Bit 7, Red LED Port E Bit 0, Red LED 26 Port D Bit 5, Green LED Port D Bit 0, Green LED 27 Port D Bit 4, OutputCapture pin Port D Bit 1, OutputCapture pin Vcc Power, common with pin 21 Power, common with pin 21 Reset Reset, common with pin 22 Reset, common with pin 22 SCK SPI Clock SPI Clock MISO SPI Master In Slave Out SPI Master In Slave Out MOSI SPI Master Out Slave In SPI Master Out Slave In Gnd Ground, common with pins 4 and 23 Ground, common with pins 4 and 23 CS On-board EEPROM Chip Select or Slave Select for SPI Slave Select for SPI