Rainbow Electronics MAX5971B - Manual (Page 37)

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MAX5971B
Single-Port, 40W, IEEE 802.3af/at,
PSE Controller with I 2 C
Switch Mode Register (R1Fh)
The switch mode register (R1Fh, Table 31) is used to
enable the watchdog timer, interrupt, and watchdog
expiry port state. On a power-up or after a reset condi-
tion, this register is set to a default value of 0x00h.
Set EN_WHDOG (R1Fh[7], Table 31) to 1 to enable
the watchdog function. When the watchdog counter
reaches zero, the hardware-controlled mode activates
and sets the port to the operating mode determined by
the HWMODE bit (R1Fh[0]). A 0 in HWMODE places
the port into shutdown mode by setting the P_M[1:0]
bits (R12h[1:0]) to 00. A 1 in HWMODE places the port
into auto mode by setting the P_M[1:0] bits to 11. If
WD_INT_EN is set to 1, an interrupt is sent if the SMODE
bit is set.
Special and Reserved Registers
(R20h to R2Fh)
Reserved Registers
(R20h to R22h, R25h to R28h, and R2Bh to R2Fh)
These registers are reserved. Writing to these registers
is not recommended as they are internally connected. If
the software needs to do a large batch write command
using the address autoincrement function, write a code
of 0x00h to these registers to safely autoincrement past
them, and then continue the write commands as normal.
Program Register (R23h)
The program register (R23h, Table 32) is used to enable
large capacitor detection, skipping detection in AUTO
mode and for setting the AC disconnect threshold. On a
power-up or after a reset condition, this register is set to
a default value of 00x0 to 0100.
CLC_EN (R23h[5]) enables the large capacitor detec-
tion feature. The CLC_EN register can be programmed
directly by the software or by using the LEGACY input
(see the High Capacitance Detection section). When
CLC_EN = 1 the device can recognize a capacitor load
up to 47FF, typ. If the CLC_EN = 0, the MAX5971B per-
forms normal detection.
DET_BY (R23h[4]) is used to allow the port to power
when skipping the detection routine in auto mode. When
DET_BY is set to 0 (default), the port cannot power up
if the port detection sequence was bypassed in auto
Table 31. Switch Mode Register
Table 32. Program Register
ADDRESS = 23h
DESCRIPTION
SYMBOL BIT NO. R/W
Reserved
7 R/W
Internally connected. For a write command, always write a zero to this bit.
6 R/W
CLC_EN 5 R/W Large capacitor detection enable
DET_BY 4 R/W Enables skipping detection in auto mode
Reserved 3 — Reserved
AC_TH
2 R/W AC_TH[2]
1 R/W AC_TH[1]
0 R/W AC_TH[0]
ADDRESS = 1Fh
DESCRIPTION
SYMBOL BIT NO. R/W
EN_WHDOG 7 R/W A logic-high enables the watchdog function
WD_INT_EN 6 R/W Enables interrupt on SMODE bit
Reserved 5 — Reserved
Reserved 4 — Reserved
Reserved 3 — Reserved
Reserved 2 — Reserved
Reserved 1 — Reserved
HWMODE 0 R/W
Port switches to auto mode if logic-high and to shutdown mode if logic-low when watchdog
timer expires