Data Flow Control - Lexmark FORMS 249X Technical Reference

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When No parity is selected, the pritner expects no parity bit when it receives

data. The printer transmits data without parity bits.

When Ignore parity is selected, the printer expects a parity bit when it receives a

data frame. Although the printer expects a parity bit, it ignores the bit and does

not check for a parity error condition. The printer uses even parity when it

transmits data.

Errors

The serial interface recognizes the following three error conditions: Parity Error,

Framing Error, and Buffer Overrun.

When a parity error is detected, the interface prints an upside down question

mark. Although the printer continues to receive data, it prints an upside down

question mark for each byte that has a parity error.

A framing error is similar to a parity error. When a framing error is detected, the

interface also prints an upside down question mark and continues to receive

data. However, unlike a parity error which causes the interface to print question

marks only for the bytes with incorrect parity, a framing error causes the

interface to print question marks for all bytes transmitted.

A buffer overrun error occurs when the host does not obey the selected protocol

and continues to send data even after the buffer is full. The buffer can only hold

128 bytes of data after the printer signals that it is busy. If the host sends more

than this amount, the data is lost and a buffer overrun error occurs.