KSZ8993M-EVAL Micrel Inc, KSZ8993M-EVAL Datasheet - Page 44

• Manufacturer Part Number: KSZ8993M-EVAL
• Description: KSZ8993M Evaluation Board - For Experimental Use Only
• Manufacturer: Micrel Inc

Specifications of KSZ8993M-EVAL

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Loopback Support
The KSZ8993M provides loopback support for remote diagnostic of failure. In loopback mode, the speed at both
PHY ports needs to be set to 100BASE-TX, and the “Priority Buffer reserve” bit needs to be set to 48 pre-
allocated buffers per output queue. The latter is required to prevent loopback packet drops and is achieved by
setting register 4 bit 0 to ‘1’.
Bit 0 of registers 29 and 45 is used to enable loopback for ports 1 and 2, respectively.
Alternatively, the MII Management register 0, bit 14 can be used to enable loopback.
Loopback is conducted between the KSZ8993M’s two PHY ports. The loopback path starts at the “Originating.”
PHY ports receive inputs (RXP/RXM), wraps around at the “loopback” PHY port’s PMD/PMA, and ends at the
“Originating” PHY port’s transmit outputs (TXP/TXM). The KSZ8993M loopback path is illustrated in the following
figure.
Micrel, Inc.
October 2008
Figure 12. Loopback Path
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KSZ8993M/ML