Motorola MPC8260 - Manual (Page 683)

MOTOROLA Chapter 24. SCC Ethernet Mode 24-15
Part IV. Communications Processor Module
Table 24-4 describes reception errors.
24.17 Ethernet Mode Register (PSMR)
In Ethernet mode, the protocol-speciÞc mode register (PSMR), shown in Figure 24-5, is
used as the Ethernet mode register.
Heartbeat Some transceivers have a heartbeat (signal-quality error) self-test. To signify a good self-test,
the transceiver indicates a collision to the
MPC8260 within 20 clocks after the Ethernet
controller sends a frame. This heartbeat condition does not imply a collision error, but that the
transceiver seems to be functioning properly. If SCCE[HBC] = 1 and the
MPC8260 does not
detect a heartbeat condition after sending a frame, a heartbeat error occurs; the channel
closes the buffer, sets the HB bit in the TxBD, and generates the TXE interrupt if it is enabled.
Table 24-5. Reception Errors
Error Description
Overrun The Ethernet controller maintains an internal FIFO for receiving data. When it overruns, the channel
writes the received byte over the previously received byte. The previous byte and frame status are lost.
The channel closes the buffer, sets RxBD[OV] and SCCE[RXF], and increments the discarded frame
counter (DISFC). The receiver then enters hunt mode.
Busy A frame was received and discarded because of a lack of buffers. The channel sets SCCE[BSY] and
increments DISFC. The receiver then enters hunt mode.
Non-Octet
Error
(Dribbling
Bits) The Ethernet controller handles up to seven dribbling bits when the receive frame terminates nonoctet
aligned. It checks the CRC of the frame on the last octet boundary. If there is a CRC error, a frame
nonoctet aligned error is reported, SCCE[RXF] is set, and the alignment error counter is incremented. If
there is no CRC error, no error is reported. The receiver then enters hunt mode.
CRC When a CRC error occurs, the channel closes the buffer, sets SCCE[RXF] and CR in the RxBD, and
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 CRC errors can be ignored if checking is not required.
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Field HBC FC RSH IAM CRC PRO BRO SBT LPB Ñ LCW NIB FDE
Reset 0000_0000_0000_0000
R/W R/W
Addr 0x11A08 (PSMR1); 0x11A28 (PSMR2); 0x11A48 (PSMR3); 0x11A68 (PSMR4)
Figure 24-5. Ethernet Mode Register (PSMR)
Table 24-4. Transmission Errors (Continued)
Error Description