Lexmark Forms Printer 2480 Technical Reference - Page 101

Errors, Data Flow Control, DTR Protocol Timing

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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. 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

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101
Section 6: Using the Printer Interface
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