[nousermane]

If you want to communicate with standard Ethernet gear, that would be either 10Mbit/s exactly (10BASE-T standard) and 100Mbit/s exactly (100BASE-TX standard).

OP implemented 10BASE-T here. Next step up is 100BASE-TX, which nobody did in software/bit-bang as of yet, as far as I'm aware - part of the reason it's fairly large jump in complexity. Namely, you'd need 3 analog voltage levels, as well as pretty hairy digital scrambling/encoding, to output 100BASE-TX. RPi-pico might just be able to eek that out with few external resistors and enough elbow grease.

Other reason nobody bothered with bit-bang 100BASE-TX - virtually all switches will happily down-negotiage to 10BASE-T, which gives you ~1.2MB/s, and that's plenty fast enough for a microcontroller with mere kilobytes of RAM.