KSZ8851SNL-BBE-EVAL Micrel Inc, KSZ8851SNL-BBE-EVAL Datasheet - Page 20

• Manufacturer Part Number: KSZ8851SNL-BBE-EVAL
• Description: BOARD EVAL MAC/PHY FOR KSZ8851
• Manufacturer: Micrel Inc
• Series: LinkMD®r

Specifications of KSZ8851SNL-BBE-EVAL

• Design Resources: BeagleBoard Zippy2
• Main Purpose: Interface, Ethernet Controller (PHY and MAC)
• Embedded: No
• Utilized Ic / Part: KSZ8851SNL
• Primary Attributes: 1 Port, 100BASE-TX/10BASE-T
• Secondary Attributes: SPI Interface, LinkMD Cable Diagnostics
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-3602; KSZ8851SNL-BBE-EVL; ZIPPY2

Micrel, Inc.
KSZ8851SNL/SNLI
Usage
®
LinkMD
can be run at any time by ensuring that Auto-MDIX has been disabled. To disable Auto-MDIX, write a ‘1’ to
®
P1CR[10] to enable manual control over the pair used to transmit the LinkMD
pulse. The self-clearing cable diagnostic
test enable bit, P1SCLMD [12], is set to ‘1’ to start the test on this pair.
When bit P1SCLMD[12] returns to ‘0’, the test is complete. The test result is returned in bits P1SCLMD[14:13] and the
distance is returned in bits P1SCLMD[8:0]. The cable diagnostic test results are as follows:
00 = Valid test, normal condition
01 = Valid test, open circuit in cable
10 = Valid test, short circuit in cable
®
11 = Invalid test, LinkMD
failed
If P1SCLMD[14:13]=11, this indicates an invalid test, and occurs when the KSZ8851SNL is unable to shut down the link
partner. In this instance, the test is not run, as it is not possible for the KSZ8851SNL to determine if the detected signal is
a reflection of the signal generated or a signal from another source.
Cable distance can be approximated by the following formula:
P1SCLMD[8:0] x 0.4m for port 1 cable distance
This constant may be calibrated for different cabling conditions, including cables with a velocity of propagation that varies
significantly from the norm.
Media Access Control (MAC) Operation
The KSZ8851SNL strictly abides by IEEE 802.3 standards to maximize compatibility.
Inter Packet Gap (IPG)
If a frame is successfully transmitted, then the minimum 96-bit time for IPG is measured between two consecutive
packets. If the current packet is experiencing collisions, the minimum 96-bit time for IPG is measured from carrier sense
(CRS) to the next transmit packet.
Back-Off Algorithm
The KSZ8851SNL implements the IEEE standard 802.3 binary exponential back-off algorithm in half-duplex mode. After
16 collisions, the packet is dropped.
Late Collision
If a transmit packet experiences collisions after 512 bit times of the transmission, the packet is dropped.
Flow Control
The KSZ8851SNL supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8851SNL receives a pause control frame, the KSZ8851SNL will not transmit the next
normal frame until the timer, specified in the pause control frame, expires. If another pause frame is received before the
current timer expires, the timer will be updated with the new value in the second pause frame. During this period (while it
is flow controlled), only flow control packets from the KSZ8851SNL are transmitted.
On the transmit side, the KSZ8851SNL has intelligent and efficient ways to determine when to invoke flow control. The
flow control is based on availability of the system resources.
There are three programmable low watermark register FCLWR (0xB0), high watermark register FCHWR (0xB2) and
overrun watermark register FCOWR (0xB4) for flow control in RXQ FIFO. The KSZ8851SNL will send PAUSE frame
when the RXQ buffer hit the high watermark level (default 3.072 KByte available) and stop PAUSE frame when the RXQ
buffer hit the low watermark level (default 5.12 KByte available). The KSZ8851SNL will drop packet when the RXQ buffer
hit the overrun watermark level (default 256-Byte available).
The KSZ8851SNL issues a flow control frame (Xoff, or transmitter off), containing the maximum pause time defined in
IEEE standard 802.3x. Once the resource is freed up, the KSZ8851SNL sends out the another flow control frame (Xon, or
August 2009
20
M9999-083109-2.0