UART

The WonderSwan's EXT port features an UART operating with the following configuration:

• 9,600 or 38,400 bps (bauds per second),
• 8N1 (8 data bits followed by 1 stop bit, no parity).

This allows for an effective maximum transfer speed of ~1066 or ~4266 bytes per second, respectively.

The hardware also features a one-byte transmit and receive buffer, which allows for a slight delay in code when handling data to/from the console.

Interrupts

The UART features two interrupts:

• UART Send Ready - constantly active while the transmit buffer is empty (Serial Control bit 2),
• UART Receive Ready - constantly active while the receive buffer contains a byte (Serial Control bit 0).

I/O ports

Serial Data

7  bit  0
---- ----
dddd dddd
|||| ||||
++++-++++- Read a byte from the transmit buffer;
           Write a byte into the receive buffer.

Serial Control

7  bit  0
---- ----
ebO. .tor
|||   ||+- 1 if the receive buffer contains a byte
|||   |+-- 1 on overrun (receive buffer overflow)
|||   +--- 1 if the transmit buffer is empty (can transmit another byte)
||+------- Write 1 to reset overrun
|+-------- UART speed: 0 = 9600 bps, 1 = 38400 bps
+--------- UART enable: 0 = off, 1 = on