
126
Agere Systems Inc.
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
Data Sheet
July 2001
11 10/100 2-Port Repeater and Backplane Segment Controller
(continued)
11.1.4 Receive Path
The following are the two functional blocks between the PHY MII and backplane interfaces in the receive path:
I
Elasticity buffer (EB). The elasticity buffer is used to retime the data before it is sent to the backplane. In
100 Mbits/s mode, the data exiting the EB is synchronous to the
MSTCLK
. In 10 Mbits/s mode, data is synchro-
nized to
CLK10
.
I
Receive control interface. The receive control interface provides a point of control for the repeater state machine
over the received data stream.
11.1.5 Transmit Path
The transmit path consists of the transmit control interface that provides a point of control for the repeater state
machine over the transmitted data stream.
TX_CLK
from the PHY, or optionally an internally generated 25 MHz
clock, is used to clock out data to the PHY.
11.2 Input Clocks
Two clocks are required to operate the backplane segment. These clocks are also required to operate the repeater
slice.
I
The 10 MHz clock should be phase-aligned to the repeater slice’s 10 MHz clock within ±1 ns.
I
The 25 MHz clock’s input must be phase-aligned to the repeater slice’s 25 MHz input. The rising edge of the
25 MHz clock should not be skewed by more than ±1 ns between the repeater slice and the backplane segment
devices.
11.3 Repeater Slice Theory of Operation
11.3.1 Repeater Core
IEEE
802.3 clause 27, defines seven applicable state diagrams that describe the intended behavior of a
100Base-X repeater. They are the repeater core, receive, transmit, carrier integrity monitor, receive timer, partition,
and repeater data handler. The repeater slice, in conjunction with the PHY and an external switch matrix, provides
a complete implementation of the functionality described by these state machines.
11.3.2 10/100 Mbits/s Operation
The repeater core of the repeater slice has been designed to work at both 25 MHz and 10 MHz under control of the
SPD_SEL
input pin
(see Table 110 on page 129)
. Whenever the value of this pin changes, the repeater core is
automatically reset and resynchronized to the new clock. This ensures that the logic returns to a known state
before the start of operation at the new frequency. The repeater slice also checks the frequency of
RX_CLK
(receive clock) to verify that it is correct for the selected speed. The detected speed is reflected in the
DS
bit of the
global port status register
(see Table 121 on page 141)
. The repeater slice can be configured via the
ASMP
bit of
the
port configuration register 1
(see Table 118 on page 138)
so that if a speed mismatch is detected, (i.e., the
DS
bit and the
SPD_SEL
are different), the port will be isolated from the repeater.