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Communication Processor Module
16-300
MPC823 USER’S MANUAL
MOTOROLA
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
16.9.21.5 SCC2 TRANSPARENT PARAMETER RAM MEMORY MAP. In totally
Transparent mode, the serial communication controller overlays the structure used in
CRC_P—For the 16-bit CRC-CCITT, CRC_P should be initialized with 0x0000FFFF.
For the 32-bit CRC-CCITT, CRC_P should be initialized with 0xFFFFFFFF and for the
CRC-16, CRC_P should be initialized with ones (0x0000FFFF) or zeros (0x00000000).
CRC_C—For the 16-bit CRC-CCITT, CRC_C should be initialized with 0x0000F0B8.
For the 32-bit CRC-CCITT, CRC_C should be initialized with 0xDEBB20E3 and for the
CRC-16 which is normally used with BISYNC, CRC_C should be initialized with
0x00000000.
16.9.21.6 SCC2 TRANSPARENT COMMANDS. You can program the CPM command
STOP TRANSMIT—After the hardware or software is reset and the channel is enabled
in the SCC2 mode register, the channel is in transmit enable mode and starts polling
the first buffer descriptor in the table every 64 clocks or immediately if the TOD bit of
the TODR is set. This command disables the transmission of frames on the transmit
channel and if the transparent controller receives it during frame transmission, buffer
transmission is aborted after a maximum of 64 additional bits and the transmit FIFO is
flushed. The TBPTR is not advanced, no new buffer descriptor is accessed and no new
buffers are transmitted for this channel. The transmitter will send idles.
Table 16-29. SCC2 Transparent Parameter RAM Memory Map
ADDRESS
NAME
WIDTH
DESCRIPTION
SCC2 Base + 30
CRC_P
Long
CRC Preset for Totally Transparent Mode
SCC2 Base + 34
CRC_C
Long
CRC Constant for Totally Transparent Receiver
NOTE: You are only responsible for initializing the items in bold.
SCC2 Base = (IMMR & 0xFFFF0000) + 0x3D00.
Note: CRC-C overlaps with the CRC constant for the HDLC-based protocols. However,
this overlap is not detrimental since the CRC constant is only used for the
receiver, so only one entry is required. You can choose an HDLC transmitter with
a transparent receiver or a transparent transmitter with an HDLC receiver.