KSZ8841-16MVLI TR Micrel, KSZ8841-16MVLI TR Datasheet - Page 32

• Manufacturer Part Number: KSZ8841-16MVLI TR
• Description: Ethernet ICs Single Ethernet Port + Generic (8, 16-bit) bus interface(Lead Free)
• Manufacturer: Micrel

Specifications of KSZ8841-16MVLI TR

• Rohs: yes
• Product: Ethernet Controllers
• Package / Case: LQFP-128
• Mounting Style: SMD/SMT

Micrel, Inc.
KSZ8841-16/32 MQL/MVL/MBL
LinkMD Cable Diagnostics
The KSZ8841M LinkMD uses time domain reflectometry (TDR) to analyze the cabling plant for common cabling problems
such as open circuits, short circuits, and impedance mismatches.
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 – fiber-optic operation is not supported.
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 ensuring that 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:
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 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, 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 KSZ8841M 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 KSZ8841M supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8841M receives a pause control frame, the KSZ8841M 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 KSZ8841M are transmitted.
On the transmit side, the KSZ8841M has intelligent and efficient ways to determine when to invoke flow control. The flow
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