Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-307
COMMUNICATION
16
SCCs
16.9.21.5 SCCx TRANSPARENT PARAMETER RAM MEMORY MAP. In totally
Transparent mode, a serial communication controller overlays the structure used in
Table 16-24 with the transparent parameters described in Table 16-29.
• CRC_P—For the 16-bit CRC-CCITT, CRC_P must be initialized with 0x0000FFFF. For
the 32-bit CRC-CCITT, CRC_P must be initialized with 0xFFFFFFFF and for CRC-16,
CRC_P must be initialized with ones (0x0000FFFF) or zeros (0x00000000).
• CRC_C—For the 16-bit CRC-CCITT, CRC_C must be initialized with 0x0000F0B8. For
the 32-bit CRC-CCITT, CRC_C must be initialized with 0xDEBB20E3 and for CRC-16,
which is normally used with BISYNC, CRC_C must be initialized with 0x00000000.
16.9.21.6 SCCx TRANSPARENT COMMANDS. You can program the CPM command
register (CPCR) with the following commands to transmit data. See Section 16.2.6.1 CPM
Command Register for additional information.
• STOP TRANSMIT—After the hardware or software is reset and the channel is enabled
in the SCCx 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 SCCx 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. SCCx Transparent Parameter RAM Memory Map
ADDRESS NAME WIDTH DESCRIPTION
SCCx Base + 30 CRC_P Long CRC Preset for Totally Transparent Mode
SCCx Base + 34 CRC_C Long CRC Constant for Totally Transparent Receiver
NOTE: You are only responsible for initializing the items in bold.
SCCx Base = (IMMR & 0xFFFF0000) + 0x3D00 (SCC2) and 0x3E00 (SCC3).
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.
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