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131 Expansion Pins Pin Description 25 Port D Bit 7, Red LED 26 Port D Bit 5, Green LED 27 Port D Bit 4, OutputCapture pin Vcc Power, common with pin 21 Reset Reset, common with pin 22 SCK SPI Clock MISO SPI Master In Slave Out MOSI SPI Master Out Slave In Gnd Ground, common with pins 4 and 23 CS Program Memory Chip Select Detailed Pin Descriptions Pin 25, Port D Bit 7 This pin drives the red LED and may also be used for PWM generation based on Timer 2. See the Atmel ATmega32, ATmega644 or ATmega644p documentation for more details on the latter function. Pin 26, Port D Bit 5 This pin drives the green LED and may also be used for PWM generation based on Timer 1. See the Atmel ATmega32, ATmega644 or ATmega644p documentation for more details on the latter function. Pin 27, Port D Bit 4 This pin is the output point for the standard OutputCapture() routine. It may also be used for PWM generation based on Timer 1. See the Atmel ATmega32, ATmega644 or ATmega644p documentation for more details on the latter function. SCK, MISO, MOSI These pins are the inputs and outputs for the SPI bus by which external SPI devices may be connected to the ZX-24/ZX-24a. Vcc, Reset, Gnd, CS These pins are used in the manufacturing and testing processes.