You need to increase the input buffer size if the buffer fills up faster than your application can read from it, as indicated by overrun errors and lost data. To prevent such errors, the Disk Driver and other system software components are designed to store any data received by the modem port while they have interrupts disabled, and then pass this data to the port's input driver. Because the system software only monitors the modem port, the printer port is not recommended for two-way communication at data rates above 300 baud. Note AppleTalk is not subject to the same limitations because it is not interrupt-driven and does not use the Serial Driver. Software overrun errors occur when an input driver's buffer overflows, usually because the application doesn't issue read calls to the driver often enough.
Parity errors occur when the serial hardware detects an incorrect parity bit.
Framing errors occur when the serial hardware detects an error in the stop bits. Break errors occur when a break signal is received. Overrun, parity, and framing errors are usually handled by requesting that the sender retransmit the affected data. Break errors are typically initiated by the user and handled as appropriate for the particular application. When an input driver receives a break signal, it terminates any pending read requests.