How many GPIO pins are on the FPGA?

The number of GPIO (General-Purpose Input/Output) pins on an FPGA depends on the specific FPGA model and package. Here’s how to find out:

1. Check the FPGA Datasheet
Every FPGA has a datasheet that lists:

• Total number of user I/O pins (varies by package size).
• Dedicated pins (e.g., configuration, clock, power).
• Bank-wise distribution (important for voltage compatibility).

Example FPGAs:

🔹 Note: Some pins are dedicated (e.g., for programming, clocks, or power), reducing available GPIOs.

2. Factors Affecting Usable GPIOs
Package Type

• Larger packages (e.g., BGA, TQFP) have more pins.
• Tiny packages (e.g., QFN, CSP) have fewer.

Bank Voltage Constraints

• FPGAs group I/O into banks, each supporting a specific voltage (e.g., 1.2V, 3.3V).
• Mixing voltages may reduce usable GPIOs.

Special Pins

Some pins are dedicated to:

• Clock inputs (PLL_CLKIN).
• Configuration (PROG_B, TMS, TDI).
• Power/GND.

3. How to Find GPIO Count for Your FPGA

1. Look up the part number (e.g., XC7A35T-1FTG256C).
2. Check the datasheet (e.g., Xilinx’s DS181).
3. Search for "Pinout Table" or "I/O Banking."

Example: Xilinx Artix-7 XC7A35T in FTG256 Package

• Total I/O pins: 200 (approx).
• Dedicated pins: ~20 (configuration, clocks).
• Usable GPIOs: ~180.

4. Tools to Estimate GPIOs
Vendor Pinout Tools

• Xilinx: Pinout & Configuration (PCF) files.
• Intel: Pin Planner (in Quartus).
• Lattice: Diamond/ICEcube2 Pin Mapper.

Schematic Review

If designing a PCB, check the FPGA footprint for available GPIOs.

5. Maximizing GPIO Availability

• Use multiplexing (e.g., time-share pins for multiple functions).
• Use serial interfaces (SPI, I2C) to reduce pin count.
• Avoid dedicated pins unless necessary.

6. Common Pitfalls

• Unusable GPIOs: Some pins are bonded out only in certain packages (e.g., BGA vs. QFP).
• Voltage conflicts: Mixing 3.3V and 1.8V in the same bank may limit GPIOs.

Conclusion

• Small FPGAs: ~20–50 GPIOs (e.g., Lattice iCE40).
• Mid-range FPGAs: ~50–200 GPIOs (e.g., Artix-7).
• High-end FPGAs: 200+ GPIOs (e.g., Kintex/Virtex).

Always check the datasheet for exact numbers!