Datasheet

DP83849IF
www.ti.com SNOSAX8D –JUNE 2009–REVISED APRIL 2013
• RMII Mode: Both Channels must have RMII Mode enabled or disabled concurrently due to the internal
reference clocking scheme. In Full Port Swap Mode, Channels are not required to have a common
speed.
• 10Base-T Serial Mode: This MAC-side mode, also known as Serial Network Interface (SNI), may not
be used when both channels share data connections (Extender/Media Converter or Broadcast TX MII
Port). This is due to the requirement of synchronous operation between channels, which is not
supported in SNI Mode.
• CRS Assignment: When a channel is not in RMII Mode, its associated CRS pin is sourced from the
transmitter and controlled by the TX MII Port Assignment, bits [10:9] of RBR (17h). When a channel is
in RMII Mode, the associated CRS pin is sourced from the receiver and controlled by the RX MII Port
Assignment, bits [12:11] of RBR (17h).
• Output Enables: Flexible MII Port Assignment does not control signal output enables.
• Test Modes: Test modes are not designed to be compatible with Flexible MII Port Selection, which
assumes default MII pin directions.
• LED Assignment: LEDs are associated with their respective digital channels, and therefore do not get
mapped to alternate channels. For example, assertion of LED_LINK_A indicates valid link status for
Channel A independent of the MII Port Assignment.
• Straps: Strap pins are always associated with their respective channel, i.e. a strap on RX_ER_A is
used by Channel A.
• Port Isolate Mode: Each MII port’s Isolate function, bit 10 of BMCR (00h) is always associated with its
respective channel, i.e. the Isolate function for Port A is always controlled by Channel A’s BMCR (00h).
Due to the various possible combinations of TX and RX port selection, it may not be advisable to place
a port in Isolate mode.
• Energy Detect and Powerdown Modes: The output enables for each MII port are always controlled
by the respective channel Energy Detect and Powerdown functions. These functions should be
disabled whenever an MII port is in use but not assigned to its default channel. Note that
Extender/Media Converter modes allow the use of Energy Detect and Powerdown modes if the RX MII
ports are not in use.
6.6 802.3u MII SERIAL MANAGEMENT INTERFACE
6.6.1 Serial Management Register Access
The serial management MII specification defines a set of thirty-two 16-bit status and control registers that
are accessible through the management interface pins MDC and MDIO. The DP83849IF implements all
the required MII registers as well as several optional registers. These registers are fully described in
Section 10. A description of the serial management access protocol follows.
6.6.2 Serial Management Access Protocol
The serial control interface consists of two pins, Management Data Clock (MDC) and Management Data
Input/Output (MDIO). MDC has a maximum clock rate of 25 MHz and no minimum rate. The MDIO line is
bi-directional and may be shared by up to 32 devices. The MDIO frame format is shown below in
Table 6-9.
Table 6-9. Typical MDIO Frame Format
MII Management Serial Protocol <idle><start><op code><device addr><reg addr><turnaround><data><idle>
Read Operation <idle><01><10><AAAAA><RRRRR><Z0><xxxx xxxx xxxx xxxx><idle>
Write Operation <idle><01><01><AAAAA><RRRRR><10><xxxx xxxx xxxx xxxx><idle>
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