Motorola MPC823e Reference Manual page 791

• Non-Octet Error (Dribbling Bits) — The SCCx Ethernet controller handles up to seven
dribbling bits when the receive frame terminates nonoctet aligned and it checks the
CRC of the frame on the last octet boundary. If there is a CRC error, then the frame
nonoctet aligned error is reported, the RXF bit is set, and the alignment error counter is
incremented. If there is no CRC error, then no error is reported.
• CRC Error—When a CRC error occurs, the channel closes the buffer, sets the CR bit
in the RX buffer descriptor, and the RXF bit in the SCCE–Ethernet register. The channel
also increments the CRC error counter (CRCEC). After receiving a frame with a CRC
error, the receiver enters hunt mode. CRC checking cannot be disabled, but the CRC
error can be ignored if checking is not required.
16.9.23 Programming the SCCx Ethernet Controller
16.9.23.1 SCCx ETHERNET MODE REGISTER. When a serial communication controller
is in Ethernet mode, the 16-bit, memory-mapped, read/write protocol-specific mode register
is referred to as the SCCx Ethernet mode register (PSMR–SCC Ethernet). Since each
protocol has specific requirements, the PSMR bits are different for each implementation.
PSMR–SCC ETHERNET
BIT 0 1 2
FIELD HBC FC RSH
RESET 0 0 0
R/W R/W R/W R/W
ADDR
HBC—Heartbeat Checking
0 = No heartbeat checking is performed. Do not wait for a collision after transmission.
1 = Wait 20 transmit clocks or 2µs for a collision asserted by the transceiver after
transmission. The HB bit in the TX buffer descriptor is set if the heartbeat is not
heard within 20 transmit clocks.
FC—Force Collision
0 = Normal operation.
1 = The channel forces a collision when each frame is transmitted. The MPC823e must
be configured in loopback operation when using this feature so that you can test
the collision logic. In the end, the retry limit for each transmit frame is exceeded.
RSH—Receive Short Frames
0 = Discard short frames that are not as long as MINFLR.
1 = Receive short frames.
MOTOROLA
3 4 5 6 7
IAM CRC PRO BRO SBT
0 0 0 0
R/W R/W R/W R/W
(IMMR & 0xFFFF0000) + 0xA28
MPC823e REFERENCE MANUAL
Communication Processor Module
8 9 10 11 12
LPB RES LCW
0 0 0 0
R/W R/W R/W R/W
13 14 15
NIB FDE
0 0
R/W R/W
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