My guess is that you aren't running on a Pi 3B or a Pi Zero W, in which case ttyS0 (uart1) has to be enabled specially. In fact, unless you are on a Compute Module there isn't much point in enabling ttyS0 because there is only one position it can appear on the 40-way header (GPIOs 14 and 15) - ttyAMA0 has the same restriction and it is a better UART.
1. In config.txt add the following line:
Code: Select all
where <x> and <y> are 14/15, 32/33 or 40/41 (or you can mix and match if you really want to). Don't use 14 and 15 if ttyAMA0 is also enabled there.
2. In cmdline.txt add the following somewhere in the line (don't split the line):
After a reboot /dev/ttyS0 should exist. You can confirm the pin usage with "raspi-gpio get".