AM85C30 datasheet(93/194 Pages) AMD

93 / 194 page

Data Communication Modes Functional Description

AMD

4–41

DATA

CRC1

CRC2

EXTERNAL SYNC

SIGNAL

Figure 4–26. External SYNC Message Format

The

SYNC input falling edge (synchronized through some internal circuitry) essentially

removes the Receiver from “Hunt Mode” in which it is waiting for synchronization before

accepting Receive Data. Upon exiting “Hunt Mode”, the Receiver will begin accepting all

incoming Receive Data. To cause the Am85C30 to discontinue accepting data (i.e. notify

the Am85C30 that there is an end of frame), the “Enter Hunt Mode” command must be

issued. The SYNC line should remain low for at least the TwSY (SYNC* Pulse Width)

specification value, and may be kept low for a longer duration of time if desired.

4.10.2.5.1

SDLC External SYNC Mode

By programming WR4 as shown below both the receiver and transmitter will be placed in

SDLC mode. The only variation from normal SDLC operation will be that the

SYNC pin

will be used to start or stop the reception of a frame by forcing the receiver to act as

though a flag had been received.

D6 D5

D4 D3

D2 D1

WR4—Register Layout

4.10.2.5.2

Synchronous External SYNC Mode

By programming WR4 as shown below the transmitter will be configured for MONOSYNC

operation and the

SYNC pin will be used to start the reception of a message.

programming either of these bit

patterns specifies that only the

SYNC

pin can be used for character sync

either the

SYNC pin or a match with

the character stored in WR7 will signal

character sync

WR4—Register Layout

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