KSZ8841-16 Micrel Semiconductor, KSZ8841-16 Datasheet - Page 26

• Manufacturer Part Number: KSZ8841-16
• Description: Single-port Ethernet Mac Controller With Non-pci Interface
• Manufacturer: Micrel Semiconductor

LinkMD Cable Diag
The KSZ8841M LinkMD uses time domain reflectometry (TDR) to analyze the cabling plant for common cabling problems
such as open circuits, short circuits, and imp
LinkMD works by sending a pulse of known amplitude and duration down the MDI and MDI-X pairs and then analyzes the
shape of the reflected signal. Timing the pulse duration gives an indication of the distance to the cabling fault with a
maximum distance of 200m and an accuracy of +/–2m. Internal circuitry displays the TDR information in a user-readable
digital format in register P1VCT[8:0].
Note: cable diagnostics are only valid for copper connections – fib
Access
LinkMD is initiated by accessing register P1VCT, the LinkMD Control/Status register, in conjunction with register P1CR4,
the 100BASE-TX PHY Controller register.
Usage
LinkMD can be run at any time by making sure Auto-MDIX has been disabled. To disable Auto-MDIX, write a ‘1’ to
P1CR4[10] to enable manual control over the pair used to transmit the LinkMD pulse. The self-clearing cable diagnostic
test enable bit, P1VCT[15], is set to ‘1’ to start the test on this pair.
When bit P1VCT[15] returns to ‘0’, the test is complete. The test result is returned in bits P1VCT[14:13] and the distance
is returned in bits P1VCT[8:0]. The cable diagnostic test results are as follows:
If P1VCT[14:13]=11, this indicates an invalid test, and occurs when the KSZ8841M is unable to shut down the link partner.
In this instance, the test is not run, as it is not possible for the KSZ8841M 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:
P1VCT[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 KSZ8841M strictly abides by IEEE 802.3 standards to maximize compatibility.
Inter Packet Gap (IPG)
If a frame is successfully transmitted, 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 KSZ8841M implements the IEEE standard 802.3 binary exponential back-off algorithm in half-duplex mode. After 16
collisions, the packet is dropped.
L
If a transmit packet experiences collisions after 512 bit times of the transmission, the packet is dropped.
November 2005
Micrel Confidential
ate Collision
00 = Valid test, normal condition
01 = Valid test, open circuit in cable
10 = Valid test, short circuit in cable
11 = Invalid test, LinkMD failed
nostics
edance mismatches.
26
er-optic operation is not supported.
KSZ8841-16/32 MQL/MVL
Rev 1.3