Microcontroller User's Manual

MOTOROLA Chapter 17. Fast Ethernet Controller (FEC) 17-33
Programming Model
17.5.4.9 Receive Control Register (RCR)
The RCR is programmed by the user. The RCR controls the operational mode of the receive
block and should be written only when ECR[ETHER_EN] = 0 (initialization time).
31 27 26 16
Field — MAX_FL
Reset 0000_0101_1110_1110
R/W R/W
15 6 5 4 3 2 1 0
Field — FCE BC_REJ PROM MII_MODE DRT LOOP
Reset 0000_0000_0000_0001
R/W R/W
Address IPSBAR + 0x1084
Figure 17-12. Receive Control Register (RCR)
Table 17-21. RCR Field Descriptions
Bits Name Description
31–27 — Reserved, should be cleared.
26–16 MAX_FL Maximum frame length. Resets to decimal 1518. Length is
measured starting at DA and includes the CRC at the end of
the frame. Transmit frames longer than MAX_FL will cause
the BABT interrupt to occur. Receive Frames longer than
MAX_FL will cause the BABR interrupt to occur and will set
the LG bit in the end of frame receive buffer descriptor. The
recommended default value to be programmed by the user is
1518 or 1522 (if VLAN Tags are supported).
15–6 — Reserved, should be cleared.
5 FCE Flow control enable. If asserted, the receiver will detect
PAUSE frames. Upon PAUSE frame detection, the
transmitter will stop transmitting data frames for a given
duration.
4 BC_REJ Broadcast frame reject. If asserted, frames with DA
(destination address) = FF_FF_FF_FF_FF_FF will be
rejected unless the PROM bit is set. If both BC_REJ and
PROM = 1, then frames with broadcast DA will be accepted
and the M (MISS) bit will be set in the receive buffer
descriptor.
3 PROM Promiscuous mode. All frames are accepted regardless of
address matching.
2 MII_MODE Media independent interface mode. Selects external
interface mode. Setting this bit to one selects MII mode,
setting this bit equal to zero selects 7-wire mode (used only
for serial 10 Mbps). This bit controls the interface mode for
both transmit and receive blocks.