MAX5952CUAX+【PDF 37/50 页】IC PSE CNTRLR FOR POE 36-SSOP

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Sheet目录43

33页 34页 35页 36页 [37页]38页 39页 40页 41页

High-Power, Quad, PSE Controller

for Power-Over-Ethernet

______________________________________________________________________________________ 37

Enable the SMODE function (Table 25) by setting

EN_WHDOG (R1Fh[7]) to 1. SMODE_ bit goes high

when the watchdog counter reaches zero and the

port(s) switch over to hardware-controlled mode.

SMODE_ also goes high each and every time the soft-

ware tries to power on a port, but is denied since the

port is in hardware mode. A reset sets R1Ch = 00h.

Table 25. SMODE Enable Register

ADDRESS = 1Ch

SYMBOL

BIT

CoR

DESCRIPTION

SMODE4

CoR

Port 4 hardware control flag

SMODE3

CoR

Port 3 hardware control flag

SMODE2

CoR

Port 2 hardware control flag

SMODE1

CoR

Port 1 hardware control flag

Table 26. Watchdog Register

ADDRESS = 1Eh

SYMBOL

BIT

R/W

DESCRIPTION

R/W

WDTIME[7]

R/W

WDTIME[6]

R/W

WDTIME[5]

R/W

WDTIME[4]

R/W

WDTIME[3]

R/W

WDTIME[2]

R/W

WDTIME[1]

WDTIME

R/W

WDTIME[0]

Set EN_WHDOG (R1Fh[7]) to 1 to enable the watchdog

function. When activated, the watchdog timer counter,

WDTIME[7:0], continuously decrements toward zero

once every 164ms. Once the counter reaches zero

(also called watchdog expiry), the MAX5952 enters

hardware-controlled mode and each port shifts to a

mode set by the HWMODE_ bit in register R1Fh (Table

27). Use software to set WDTIME (Table 26) and contin-

uously set this register to some nonzero value before

the register reaches zero to prevent a watchdog expiry.

In this way, the software gracefully manages the power

to ports upon a system crash or switchover.

While in hardware-controlled mode, the MAX5952

ignores all requests to turn the power on and the flag

SMODE_ indicates that the hardware has taken control

of the MAX5952 operation. In addition, the software is

not allowed to change the mode of operation in hard-

ware-controlled mode. A reset sets R1Eh = 00h.

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