MOTOROLA
Chapter 27. SCC BISYNC Mode
27-1
Chapter 27
SCC BISYNC Mode
270
270
The byte-oriented BISYNC protocol was developed by IBM for use in networking
products. There are three classes of BISYNC framesÑtransparent, nontransparent with
header, and nontransparent without header, shown in Figure 27-1. The transparent frame
type in BISYNC is not related to transparent mode, discussed in Chapter 29, ÒSCC
Transparent Mode.Ó Transparent BISYNC mode allows full binary data to be sent with any
possible character pattern. Each class of frame starts with a standard two-octet
synchronization pattern and ends with a block check code (BCC). The end-of-text character
(ETX) is used to separate the text and BCC Þelds.
Figure 27-1. Classes of BISYNC Frames
The bulk of a frame is divided into Þelds whose meaning depends on the frame type. The
BCC is a 16-bit CRC format if 8-bit characters are used; it is a combination longitudinal
(sum check) and vertical (parity) redundancy check if 7-bit characters are used. In
transparent operation, a special character (DLE) is deÞned that tells the receiver that the
next character is text, allowing BISYNC control characters to be valid text data in a frame.
A DLE sent as data must be preceded by a DLE character. This is sometimes called
byte-stufÞng. The physical layer of the BISYNC communications link must synchronize
the receiver and transmitter, usually by sending at least one pair of synchronization
characters before each frame.
BISYNC protocol is unusual in that a transmit underrun need not be an error. If an underrun
occurs, a synchronization pattern is sent until data is again ready. In nontransparent
operation, the receiver discards additional synchronization characters (SYNCs) as they are
received. In transparent mode, DLE-SYNC pairs are discarded. Normally, for proper
Nontransparent with Header
SYN1
SYN2
SOH
Header
STX
Text
ETX
BCC
Nontransparent without Header
SYN1
SYN2
STX
Text
ETX
BCC
Transparent
SYN1
SYN2
DLE
STX
Transparent
Text
DLE
ETX
BCC
Содержание MPC860 PowerQUICC
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Страница 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
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Страница 226: ...8 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
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Страница 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
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Страница 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
Страница 326: ...IV vi MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
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Страница 998: ...37 48 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part VI Debug and Test ...
Страница 1016: ...A 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Страница 1024: ...B 8 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Страница 1030: ...C 6 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
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