Apple LaserWriter Select 310 Specifications download pdf (Page 59)

CHAPTER 3

Communication Channels

Serial Communication 47

Parity Settings 3

The parity settings for the serial channel may be odd, even, space, or mark. Table 3-2

indicates how the parity setting and number of data bits work together.

Flow Control 3

The LaserWriter Select 310 printer uses one of two conventions for controlling the ﬂow of

characters to and from the host computer. These conventions are DTR and XON/XOFF. If

the host fails to conform to the selected ﬂow control protocol, unexpected occurrences of

ioerror may result.

DTR Flow Control 3

DTR ﬂow control uses the Data Terminal Ready control signal. Normally, the printer

leaves this signal turned on. However, when it needs to stop the ﬂow of characters from

the host, it turns DTR off. The host must then immediately stop sending characters

until the printer turns DTR back on again. Similarly, another signal, Data Set Read (DSR)

may be used by the host to control the ﬂow of data sent to it from the printer. Packet DTR

is an implementation of DTR ﬂow control speciﬁcally set and used by the Apple

LaserWriter driver. It uses the DSR signal to control the ﬂow of data sent to the host in

packets of three characters at a time.

Table 3-2 Data and parity choices for the LaserWriter Select 310 printer

Data bits Parity Description

Standard Space 8 bits are sent. The 8th bit transmitted is zero, and

the 8th bit received is ignored.

Standard Odd or even 8 bits are sent. The 8th bit is used for parity.

Standard Mark 8 bits are sent and received. The parity bit is not stripped.

Since the PostScript interpreter expects ASCII data (high

bit zero), a host sending mark parity data will not be

understood, and you should select 7-bit mode in which

the parity bit is stripped.

7 bits Space 7 data bits are sent. A zero is added.

7 bits Odd or even 7 data bits are sent. A parity bit is added to the 7 data

bits in either odd or even parity, depending on the parity

setting.

7 bits Mark 7 data bits are sent. A one is added.

8 bits Space 8 bits are sent.

8 bits Odd or even 8 bits are sent. A parity bit is added to the 8 bits in either

odd or even parity, depending on the parity setting.

8 bits Mark 8 bits are sent.

NOTE Parity is checked on received characters only when the parity setting is even or odd. If a

parity error is detected the PostScript interpreter generates an ioerror.

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Apple LaserWriter Select 310 Specifications Page 59