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16.9.18.3 CONNECTING TO APPLETALK. The MPC823e connects to LocalTalk and,
using the TXDx, RTSx, and RXDx pins, is an interface for the RS-422 transceiver. The
RS-422, in turn, is an interface for the LocalTalk connector. Although it is not shown, a
passive RC circuit is recommended between the transceiver and connector. Figure 16-90
illustrates how to connect the MPC823e to LocalTalk.
MPC823e
6-BIT
TWO
TXDx
DEST
SYNC
HDLC
ADDR
SEQ
FLAGS
RTSx
STANDARD HDLC FRAME HANDLING
Figure 16-90. Connecting the MPC823e to AppleTalk
The 16x multiplier of a 3.686MHz clock can be generated from an external frequency source
or from one of the baud rate generators if the resulting output frequency is close to a multiple
of the 3.686MHz frequency. The MPC823e asserts the RTSx signal throughout the duration
of the frame so that RTSx can be used to enable the RS-422 transceiver.
MOTOROLA
MPC823
TX DATA
TXDx
SCC
TX ENABLE
RTSx
RX DATA
RXDx
SOURCE
CONTROL
ADDR
BYTE
STORED IN RECEIVE BUFFER
STORED IN TRANSMIT BUFFER
MPC823e REFERENCE MANUAL
Communication Processor Module
RS-422
MINI-DIN 8
CRC-16
DATA
16 ONES
CLOSING
(ABORT)
FLAG
16-267
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