How many GPIO pins are on the FPGA?

There is no single answer. The number of GPIO (General-Purpose Input/Output) pins on an FPGA depends entirely on the specific chip and its package.

However, I can explain exactly how to find the number for a specific FPGA and what factors determine it.

1. The Primary Factor: Package and Pinout
The biggest determinant of GPIO count is the physical package the FPGA chip comes in.

• Small, Low-Cost FPGAs: Might come in a package with as few as 32 pins, with perhaps 20 of them usable as GPIO.

Example: Lattice iCE40UP5K in a 48-pin QFN package has 39 GPIOs.

• Mid-Range FPGAs: Typically come in packages with hundreds of pins.

Example: AMD Xilinx Artix-7 in a FTG256 package has 150 user I/Os.

• High-End FPGAs: Can come in massive packages with over a thousand pins.

Example: Intel Stratix 10 in a 1932-ball BGA package can have over 1,000 user I/Os.

Why such variation? Larger, more expensive packages allow for more physical connections to the silicon die inside. The manufacturer will create several versions of the same FPGA silicon die in different packages to target different cost and performance points.

2. Not All Pins Are GPIO
The total pin count of the package is a maximum. Not all these pins are available for you to use as general-purpose I/O. They are divided into several groups:

• Power Pins (VCCINT, VCCAUX, VCCO): The largest group. The FPGA core and I/O banks need many pins for stable power delivery. A large FPGA can have 100+ pins dedicated just to power and ground.
• Configuration Pins: Dedicated pins for programming the FPGA (e.g., PROGRAM_B, INIT_B, DONE, JTAG pins like TDI, TDO, TCK, TMS).
• Clock Input Pins: Dedicated "clock-capable" input pins (CCIOs) that have a high-quality path to the global clock routing resources.
• Dedicated Function Pins: Pins for specific high-speed transceivers (GTX/GTH/GTY), PCIe, Ethernet, or memory interfaces (DDR). These are not GPIO.

The remaining pins are the User I/O or GPIO.

How to Find the Exact Number for a Specific FPGA
You must look at the manufacturer's documentation for the exact part number. Here is the step-by-step process:

1. Identify the Full Part Number.
This is more than just the family (e.g., "Artix-7"). You need the full code, for example: XC7A35T-1FTG256C

• XC7A35T: Artix-7 35T Logic Fabric
• 1: Speed Grade
• FTG256: Package Type (This is the critical part! A 256-ball Fine-Pitch BGA)
• C: Commercial Temperature Grade

2. Find the "Pinout File" or "Product Specification".
Search for " Pinout" or " Product Table".

• For AMD/Xilinx: Look for the "Pinout Files" tab on the product page or the "7 Series Packaging and Pinouts" user guide (UG475).
• For Intel/Altera: Look for the "Device Pin-Out Files" or the "Pin Connection Guidelines".

3. Read the Summary Table.
These documents will have a master table. For our example, XC7A35T-1FTG256C, the table will show:

This tells you that this specific FPGA has 150 GPIO pins available.

4. (For Board Designers) Consult the "Pinout Utility".
Both AMD and Intel offer interactive web-based or software-based tools where you input your part number, and it shows you a detailed, pin-by-pin breakdown of every function.

Key Concepts Related to FPGA GPIO

• I/O Banks: FPGA GPIO pins are organized into groups called I/O Banks. Each bank can have its own I/O voltage standard (VCCO). This is why an FPGA can interface with 3.3V, 2.5V, and 1.8V devices simultaneously.
• HP vs. HR Banks: In newer FPGAs, there are High-Performance (HP) and High-Range (HR) banks. HP banks support faster, lower-voltage standards, while HR banks support a wider range of older voltages.
• Programmability: The true power of FPGA GPIO is that each pin's characteristics (voltage standard, slew rate, drive strength, pull-up/pull-down) are programmable in your design software (Vivado/Quartus).

Summary

So, if someone asks you this question, the correct response is: "Which specific FPGA part number are you referring to?"