The UART and the ESP WiFi Module

Synopsis

The Next has a UART wired to an on-board socket where, on real hardware, an ESP-01 WiFi module lives. The same UART is also exposed as a generic serial port — perfect for talking to a host PC, a sensor, or any 3.3 V serial device. Klive emulates the UART surface (with a configurable virtual peer) so you can develop and test serial code without a real Next on your desk.

Topics:

• The UART ports. $133B (data), $143B (control / status). 8N1 framing only — no parity options.
• Baud rate. Set via NextReg $0A/$0B and $0E/$0F — full divider chain explained, with a table of common baud rates.
• Polled I/O. The simplest possible TX and RX loops. Status bits: TX-empty, RX-ready.
• Interrupt-driven I/O. UART RX and TX interrupts via NextRegs $C2 (enables) and $C6 (status). Building a small ring-buffer driver around them.
• Talking to the ESP. AT command basics — set network, connect to access point, open TCP, send/receive. Just enough to get “fetch a JSON file from the internet” working.
• Klive specifics. What kind of virtual peer Klive offers and how to wire it up for the exercises.

What you should know first

• I/O and NextRegs.
• Interrupts — for the ring-buffer driver.

Planned exercises

• Polled echo. Read a byte from the UART, write it back. Test with the Klive virtual peer.
• Interrupt-driven terminal. A scrolling text window that displays everything that arrives over the UART, while the main loop animates a sprite to prove it’s not blocking.
• AT hello (real hardware). Aimed at users who do have a Next with ESP — open a TCP connection and send a one-line HTTP request. Klive users can run the same code against the virtual peer to see the AT command sequence.