Three years ago, @kingyoPiyo’s Pico-10BASE-T project drew wide attention right here on Elektor for implementing 10 Mbit/s Ethernet on the Raspberry Pi Pico using just a few resistors. In 2023, another milestone followed with bit-banged USB, showing how far the RP2040’s (and now RP2350) programmable I/O could be pushed.
What Can an RP2350 Bit-Bang Next?
Now, developer Steve Markgraf (GitHub @steve-m) has extended the concept with Pico-100BASE-TX — a 100 Mbit/s Fast Ethernet transmitter running entirely in software.
Markgraf’s implementation uses the PIO and DMA to perform MLT-3 encoding, 4B5B line coding, and scrambling at a 125 MHz symbol rate. The result is a functioning 100 Mbit/s link capable of streaming about 11 Mbyte/s over UDP, demonstrated by real-time audio and ADC data streams.
As before, this is a transmit-only proof of concept and must not be connected to PoE-enabled hardware. A pulse transformer or intermediary Ethernet switch is recommended for isolation.
Check Out the Rest of His Repo
Example applications in the repository include a counter, internal-ADC streamer, and an audio demo using a PCM1802 converter at 75 kHz. The library supports both the RP2040 and the newer RP2350 (Pico 2) and builds with the standard Pico SDK.
Source: Pico-100BASE-TX on GitHub — check it in action in the video there.
Beyond the technical achievement, projects like this hint at new possibilities for low-cost, high-speed data acquisition and streaming using microcontrollers that were never designed for it. A Pico capable of pushing 11 MB/s over Ethernet could form the basis of compact, inexpensive test instruments, remote sensors, or experimental network interfaces — all without a dedicated PHY chip. As these bit-banged interfaces become faster and more capable, the question naturally follows: how far can software-defined hardware really go on a two-dollar microcontroller?
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