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Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-147
SERIAL
I/F
COMMUNICATION
16
PROCESSOR
MODULE
When the receive and transmit sections use the same clock and sync signals, these sections
should be programmed to the same configuration. Also, the L1TXDA pin in the I/O register
should be programmed to be an open-drain output. To support the monitor and C/I channels
in GCI, those channels should be routed to one of the serial management controllers. To
support the D channel when there is no possibility of collision, you should clear the GRA bit
corresponding to the serial communication controller that supports the D channel in the
SIMODE register.
16.7.7.2.2 SCIT Mode. To interface with the GCI/SCIT bus, the SIMODE register must be
programmed to GCI/SCIT mode. The serial interface RAM is programmed to support a
96-bit frame length and the frame sync is programmed to the GCI sync pulse. Generally, the
SCIT bus supports the D channel access collision mechanism. For this purpose, you should
program the receive and transmit sections to use the same clock and sync signals with the
CRTA bit and program the GRA bit to transfer the D channel grant to the serial
communication controller that supports this channel. The received bit should be marked by
programming the channel select bits of the serial interface RAM to 111 for an internal
assertion of a strobe on this bit. This bit is sampled by the serial interface and transferred to
the D channel serial communication controller as the grant. The bit is generally bit 4 of the
C/I in channel 2 of GCI, but any other bit can be selected using the serial interface RAM.
16.7.7.3 GCI INTERFACE PROGRAMMING EXAMPLE. Assuming SCC2 is connected to
the D channel, SMC2 to the B1 channel, and SMC1 to the C/I channels, the initialization
sequence is as follows:
1. Program the serial interface RAM. Write all entries that are not used with 0x0001, set
the LST bit, and disable the routing function.
ENTRY
NUMBER
RAM WORD
SWTR
SSEL
CSEL
CNT
BYT
LST
DESCRIPTION
1
0
0000
110
0000
1
0
8 Bits SMC2 (B1)
2
0
0001
000
0000
1
0
Ext Device (B2)
3
0
0000
101
0000
1
0
8 Bits SMC1 (M)
4
0
0000
010
0001
0
2 Bits SCC2 (D)
5
0
0000
101
0101
0
6 Bits SMC1 (I+A+E)
6
0
0000
000
0110
1
0
Skip 7 Bytes
7
0
0000
000
0001
0
Skip 2 Bits
8
0
0000
111
0000
0
1
D Grant Bit
Note: Since GCI requires the same routing for both receive and transmit, an exact
duplicate of the above entries should be written to both the receive and transmit
sections of the serial interface RAM beginning at addresses 0 and 128,
respectively.