mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 260

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Differences between MCF5272 FEC and MPC860T FEC
An underrun occurs when, during transmit, the transmit FIFO empties before the end of the
frame. Then, a bad CRC is appended to the partially transmitted data. In addition, the UN
bit is set in the last BD for the current frame. This situation can occur if the FEC cannot
access an internal bus, or if the next BD in the frame is not available.
11.7 Differences between MCF5272 FEC and
The MCF5272 features the same FEC as the MPC860T with a few differences. The
following list pertains to the MCF5272.
11-36
Bits
-
-
• Limited throughput full-duplex 100 Mbps operation. External bus use is the limiting
• Only big-endian mode is supported for buffer descriptors and buffers.
• Separate interrupt vectors for Rx, Tx and non-time critical interrupts
• Interrupt priority is set in the interrupt controller
• The formula for calculating E_MDC clock frequency differs between MCF5272 and
MPC860T FEC
factor.
MPC860T:
— MCF5272: E_MDC_FREQUENCY= system frequency / (4 * MII_SPEED)
— MPC860T: E_MDC_FREQUENCY= system frequency / (2 * MII_SPEED)
Tx Buffer Pointer Written by the user. The transmit buffer pointer, which contains the address of the
Data Length
Name
Anytime the software driver sets an R bit in a transmit
descriptor, the driver should immediately write to TDAR.
MCF5272 ethernet controller signal names are generally
identical to those used in the MPC860T, except for a prefix of
‘E_’. For example, MDC in the MPC860T corresponds to
E_MDC in the MCF5272.
Table 11-35. TxBD Field Descriptions (Continued)
Written by the user. Data length is the number of octets the FEC should transmit from this
BD’s data buffer. It is never modified by the FEC. Bits [10–0] are used by the DMA engine;
bits [15–11] are ignored.
associated data buffer, may be even or odd. The buffer must reside in memory external to
the FEC. This value is never modified by the FEC.
MCF5272 User’s Manual
NOTE:
NOTE:
Description
MOTOROLA