User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 9: Ethernet MACs Page
263
S e c t i o n 9 : E t h e r n e t M A C s
I
NTRODUCTION
The BCM1250 includes three Ethernet MACs. The BCM1125 and BCM1125H include two Ethernet MACs. The
MACs support the 10 Mbps, 100 Mbps and 1 Gbps Ethernet standards. They can operate in full or half-duplex
mode at all speeds. The MII (10/100 Mbps) or GMII (1 Gbps) standard interfaces are used to connect to
external PHY (physical interface) chips. The minimum and maximum size of a packet is programmable, giving
support for jumbo packets up to 16K-1 Bytes. For half-duplex operation the MAC supports programmable
backoff and retransmission following a collision. A set of RMON counters are updated automatically at the end
of each packet transmission or reception, these may be read by the CPU at any time to gather interface
statistics.
In addition to the standard Ethernet mode, each interface can be put into a bypass mode where the Ethernet
protocol processing is disabled and the interface acts as a Packet FIFO. In this the GMII pins are used to
provide an 8-bit data path in each direction that can carry packet or unframed data. Selection of Ethernet or 8-
bit Packet FIFO is done by software.
The interfaces are identical and independent. The registers and interrupts associated with each are
differentiated by appending the interface number to their names. On the BCM1250 the interfaces are
_0
,
_1
and
_2
. On the BCM1125/H the interfaces are
_0
and
_1
. Accesses made to the address range allocated to a
nonexistant MAC may cause all MACs to exhibit UNPREDICTABLE behaviour. The following sections
describe one of the MACs.
The MAC interfaces can be replaced by Packet FIFO interfaces that are 16-bits wide in each direction. Pins
from MAC E0 and E1 are reassigned to Packet FIFO interface F0 on the BCM1250 or F on the BCM1125/H,
and on the BCM1250 pins from all three MACs are reassigned to Packet FIFO interface F1. Selection between
Ethernet and Packet FIFO operation is done by software.