This project is a 24-bit digital IO expander module, using the Texas Instruments TCA6424A circuit, utilizing the I2C protocol. The design is available with two connector types: either Type-6 (I2C single-row) or Type-6A (I2C extended double-row) compatible interface per open PMOD interface standard v1.3.1 by Digilent Inc. The PMOD (peripheral module interface) standardizes connectivity with FPGA or microcontroller development boards.
In this module, 24 IO pins are controlled through the two-wire serial I2C protocol. For each individual IO pin, a corresponding LED displays its current status with negative logic. A pins logic level '0' lights up the LED, while level '1' turns it off. To fit all IO pins on a reasonably small PMOD, 0402-size SMD components have been selected. DIP switches enable I2C pull-up resistors if needed, and change the I2C bus address between 0x22 and 0x23. Two modules can be chained for a total of 48 IO signals. Three test points can be fitted for I2C bus troubleshooting.
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