Motorola MPC823e - Page 721

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-267
COMMUNICATION
16
PROCESSOR MODULE
SCCs
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.
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.
MPC823e
Figure 16-90. Connecting the MPC823e to AppleTalk
MPC823
RS-422
MINI-DIN 8
SCC
TXDx
RTSx
RXDx
TX DATA
RX DATA
TX ENABLE
16 ONES
(ABORT)
CRC-16
STORED IN TRANSMIT BUFFER
STORED IN RECEIVE BUFFER
RTSx
TXDx
DEST
ADDR
SOURCE
ADDR
CONTROL
BYTE
DATA
STANDARD HDLC FRAME HANDLING
6-BIT
SYNC
SEQ
TWO
HDLC
FLAGS
CLOSING
FLAG