SCD1284 datasheet(61/176 Pages) INTEL

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IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

5.6.4.1

Generating Service Requests with Modem Pins

The CD1284 can generate service requests when any one of the input pins changes state. Either or

both edges can be detected by setting bits in MCOR1 and MCOR2. For each pin, the user can

individually enable an on-to-off or off-to-on transition detection of the inputs. When the CD1284

detects such a transition, the corresponding bit in the MCR is set. If the corresponding IER bit in

the channel is set, the CD1284 asserts the SVCREQM* output.

The user must clear the MCR during the service request service routine before writing to the EOIR.

The CD1284 performs this task by reading the modem input signals and comparing the current

value with the value read in the last pass through the outer scanning loop. Because this is the

lowest-priority event in the CD1284 scanning loop, changes can not be detected unless they are

several hundred microseconds long.

For example, the modem input pins can be used to detect the closing of a switch. However,

consider the relatively slow speed of response when using modem input pins for this purpose. The

CD1284 does not latch the modem input signals.

5.6.4.2

Using Modem Pins as General-Purpose I/O

Since the modem pins can be directly accessed by the host, they can be used as general-purpose I/O

pins if they are not needed for flow control or modem interfacing. Simply read from and write to

these pins as with any I/O port.

5.7

Receive Special Character Processing

The CD1284 has several ways to send special characters and to process these characters when

received. Some special characters have fixed definitions and others are user-defined. Figure 9 on

page 64 defines the processing that the CD1284 performs for receive data. This flow chart

illustrates the special character handling process.

5.7.1

UNIX Character Processing

The CD1284 incorporates special character processing of particular benefit in systems designed to

run the UNIX operating system. The processing performs some of the functions normally handled

by the ‘line discipline’ part of a serial device driver program. This provides higher overall

performance in serial communication than could otherwise be obtained because character

manipulation occurs at the hardware level without any CPU interaction. This processing includes

CR (carriage return) and NL (new line) substitution, programmable response to errored characters

(framing, parity and overrun errors), the LNext function and ISTRIP. Each type of processing is

optional and can be enabled/disabled with control bits in the CORs 2, 4, and 5. The following

sections describe of each of these functions.

5.7.1.1

Line-Terminating Characters

The CD1284 can be programmed to perform automatic substitution of the CR and NL characters

on both received and transmitted data. Received character processing has five unique substitutions

based on the value of IGNCR, ICRNL, and INLCR (COR4[7:5]); some combinations cause

identical actions.

SCD1284 Datasheet(PDF) 61 Page - Intel Corporation

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