The Prizm's 2.5mm link port is a standard UART, capable of operating at up to 115200 bits per second in normal configurations. See the serial syscalls for usage information in add-ins.
Connector and Cable
The connectors on the link cable are standard 2.5 mm phone connectors with three pins. The cables are passive, free of electronic components, and arranged so that the transmission pin on one end connects to the receive pin on the other end (crossover).
From the male connector view, the sleeve is ground, the ring is the receive pin and the tip is the transmit pin.
The voltage level +4.2V is used for logical 1, and 0V for logical 0.
Through the use of serial syscalls, software can operate the serial port at ten different baud rates, from 300 baud to 115200 baud, using odd, even or no parity, one or two stop bits and seven or eight bits of data length - refer to the parameter description of Serial_Open for more information. By fiddling with the serial port registers, the serial port can be used in a more direct fashion, including higher speeds, at which reliable data transfer might not be possible.
The 3-pin port corresponds to the first serial communication interface of the SH7305, SCIF0. Its base address is 0xA4410000 and it is identical to the one found in the SH7724 and in the SH7730.
When the system PLL is reclocked, this also affects the serial bit rate (which is presumably derived from the peripheral clock). For this reason, serial communication with an over- or under- clocked device will generally not work correctly, unless the other device is similarly adjusted.
If transferring data between two overclocked Prizms, the transfer is noticeably faster, but more prone to data transmission errors.