Lexmark 248X, 249X manual 101, Errors, Data Flow Control

Models: 249X 248X

1 227
Download 227 pages 723 b
Page 101
Image 101

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.

Data Flow Control

Flow control is accomplished by way of software or the hardware DTR (Data Terminal Ready). Three flow control protocols are available:

DTR Pacing (hardware)

XON/XOFF (software)

Multi XON/XOFF (software)

DTR Protocol Timing

You use DTR to control the data flow from the computer. DTR goes from high to low to indicate to the computer that the printer cannot receive more data due to one of the following conditions:

Buffer full

Attendance error (paper out, printer error)

Printer not in ready state

Section 6: Using the Printer Interface

101

 

Page 101
Image 101
Lexmark 248X, 249X manual 101, Errors, Data Flow Control