SCD1284 datasheet(63/176 Pages) INTEL

63 / 176 page

IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

5.7.2

Non-UNIX Receive Special Character Processing

In addition to UNIX special-character processing, the CD1284 provides other special character

recognition capabilities. The CD1284 has four registers that define special characters, SCHR1–

SCHR4. SCHR1 and SCHR2, are used in flow-control activities and (see Section 5.6). SCHR3 and

SCHR4 define two additional special characters that the CD1284 can scan for in the receive data

stream. Recognition of special characters 3 and 4 are enabled by the SCD34 bit (COR3[6]). If

either of these characters are received, a special character detect (receive exception) service request

is sent. Note that if automatic in-band flow control is not enabled, SCHR1 and SCHR2 can still be

used as special characters. They are detected and reported as receive exceptions, but they do not

cause flow-control activities to be envoked.

The range detect function is another special character function. If this mode is enabled (COR3[7]

set), the CD1284 compares all received characters against the values in the SCRL and SCRH

registers. If the character received falls between these two values (inclusive), a special character

detect service request is posted.

The status shown in the RDSR indicates which of the special character recognition conditions were

met and caused the receive exception service request.

SCD1284 Datasheet(PDF) 63 Page - Intel Corporation