Rainbow-electronics MAX6871 Manual do Utilizador descarregar pdf (Página 43)

MAX6870/MAX6871

EEPROM-Programmable Hex/Quad

Power-Supply Sequencers/Supervisors with ADC

______________________________________________________________________________________ 43

Configuring the Watchdog Timers

(Registers 3Ch–3Fh)

A watchdog timer monitors microprocessor (µP) soft-

ware execution for a stalled condition and resets the µP

if it stalls. The output of a watchdog timer (one of the

programmable outputs) connects to the reset input or a

nonmaskable interrupt of the µP.

Registers 3Ch–3Fh configure the watchdog functionality

of the MAX6870/MAX6871. Program each watchdog

timer to assert one or more programmable outputs (see

Tables 10–21). Program each watchdog timer to reset on

one of the GPI_ inputs, one of the programmable out-

puts, or a combination of one GPI_ input and one pro-

grammable output.

Each watchdog timer features independent initial and

normal watchdog timeout periods. The initial watchdog

timeout period applies immediately after power-up, after a

reset event takes place, or after enabling the watchdog

timer. The initial watchdog timeout period allows the µP to

perform its initialization process. If no pulse occurs during

the initial watchdog timeout period, the µP is taking too

long to initialize, indicating a potential problem.

The normal watchdog timeout period applies in every

other cycle after the initial watchdog timeout period

occurs. The normal watchdog timeout period monitors

a pulsed output of the µP that indicates when normal

processor behavior occurs. If no pulse occurs during

the normal watchdog timeout period, this indicates that

the processor has stopped operating or is stuck in an

infinite execution loop.

Disable or enable each initial timeout period through reg-

isters 3Ch and 3Eh. Registers 3Dh and 3Fh program the

initial and normal watchdog timeout periods, and enable

or disable each watchdog timer. See Tables 27 and 28

for a summary of the watchdog behavior.

Fault Detector

Registers 60h–62h store all fault conditions, including

undervoltage, overvoltage, GPI_, and watchdog timer

faults (see Table 29). Fault registers are read-only and

lose contents upon power removal. The first read com-

mand from the fault registers after power-up gives invalid

data. Any MR assertion writes to the fault register.

Reading the fault register clears all fault flags. Both GPI_

Table 27. Watchdog Inputs (Addresses

3Ch (Watchdog 1), 3Eh (Watchdog 2))

BIT

N A M E DESCRIPTION

[1:0]

Watchd og

Inp ut

S el ecti on

00 = GPI1 input

01 = GPI2 input

10 = GPI3 input

11 = GPI4 input

[4:2]

Watchd og

Inter nal

Inp ut

S el ecti on

000 = P O1 ( M AX 6870) , not used ( M AX 6871)

001 = P O2 ( M AX 6870) , not used ( M AX 6871)

010 = P O3 ( M AX 6870) , P O1 ( M AX 6871)

011 = P O4 ( M AX 6870) , P O2 ( M AX 6871)

100 = P O5 ( M AX 6870) , P O3 ( M AX 6871)

101 = P O6 ( M AX 6870) , P O4 ( M AX 6871)

110 = P O7 ( M AX 6870) , P O5 ( M AX 6871)

111 = P O8 ( M AX 6870) , not used ( M AX 6871)

[6:5]

Watchd og

D ep end ency

on Inp uts

00 = 11 = watchdog clear depends on

both GPI_ from 3Ch[1:0] and PO_ from

3Ch[4:2].

01 = watchdog clear depends only on

PO_ from 3Ch[4:2].

10 = watchdog clear depends only on

GPI_ from 3Ch[1:0].

[7]

Ini ti al

Watchd og

Ti m eout

E nab l e

0 = disables initial watchdog timeout

period (normal watchdog timeout not

affected).

1 = enables initial watchdog timeout

period.

Table 28. Watchdog Timeout Period

Selection (Addresses 3Dh (Watchdog 1),

3Fh (Watchdog 2))

BIT NAME DESCRIPTION

[2:0]

Normal

Watchdog

Timeout Period

000 = 6.25ms

001 = 25ms

010 = 100ms

011 = 400ms

100 = 1.6s

101 = 6.4s

110 = 25.6s

111 = 102.4s

[5:3]

Initial Watchdog

Timeout Period

(Immediately

following power-

up, reset event,

or enabling

watchdog)

000 = 6.25ms

001 = 25ms

010 = 100ms

011 = 400ms

100 = 1.6s

101 = 6.4s

110 = 25.6s

111 = 102.4s

[6]

Watchdog

Enable

0 = disables watchdog timer

1 = enables watchdog timer

[7] — Not used

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