Datasheet

 2016 Microchip Technology Inc. DS00002199A-page 11
KSZ8081RNA/RND
3.1.5 10BASE-T RECEIVE
On the receive side, input buffer and level detecting squelch circuits are used. A differential input receiver circuit and a
phase-locked loop (PLL) performs the decoding function. The Manchester-encoded data stream is separated into clock
signal and NRZ data. A squelch circuit rejects signals with levels less than 400 mV, or with short pulse widths, to prevent
noise at the RXP and RXM inputs from falsely triggering the decoder. When the input exceeds the squelch limit, the PLL
locks onto the incoming signal and the KSZ8081RNA/RND decodes a data frame. The receive clock is kept active
during idle periods between data receptions.
3.1.6 PLL CLOCK SYNTHESIZER
The KSZ8081RNA/RND in RMII – 25 MHz Clock mode generates all internal clocks and all external clocks for system
timing from an external 25 MHz crystal, oscillator, or reference clock. For the KSZ8081RNA/RND in RMII – 50 MHz
clock mode, these clocks are generated from an external 50 MHz oscillator or system clock.
3.1.7 AUTO-NEGOTIATION
The KSZ8081RNA/RND conforms to the auto-negotiation protocol, defined in Clause 28 of the IEEE 802.3 Specifica-
tion.
Auto-negotiation allows unshielded twisted pair (UTP) link partners to select the highest common mode of operation.
During auto-negotiation, link partners advertise capabilities across the UTP link to each other and then compare their
own capabilities with those they received from their link partners. The highest speed and duplex setting that is common
to the two link partners is selected as the mode of operation.
The following list shows the speed and duplex operation mode from highest to lowest priority.
• Priority 1: 100BASE-TX, full-duplex
• Priority 2: 100BASE-TX, half-duplex
• Priority 3: 10BASE-T, full-duplex
• Priority 4: 10BASE-T, half-duplex
If auto-negotiation is not supported or the KSZ8081RNA/RND link partner is forced to bypass auto-negotiation, then the
KSZ8081RNA/RND sets its operating mode by observing the signal at its receiver. This is known as parallel detection,
which allows the KSZ8081RNA/RND to establish a link by listening for a fixed signal protocol in the absence of the auto-
negotiation advertisement protocol.
Auto-negotiation is enabled by either hardware pin strapping (ANEN_SPEED, Pin 23) or software (Register 0h, Bit [12]).
By default, auto-negotiation is enabled after power-up or hardware reset. After that, auto-negotiation can be enabled or
disabled by Register 0h, Bit [12]. If auto-negotiation is disabled, the speed is set by Register 0h, Bit [13], and the duplex
is set by Register 0h, Bit [8].
The auto-negotiation link-up process is shown in Figure 3-1.