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PT0289(07/07)

Ver: 0

4

The reset output is typically connected to the reset input

of a microprocessor (P). A P’s reset input starts or

restarts the P in a known state. The PT7M7443~7452

P supervisory circuits provide the reset logic to prevent

code-execution errors during power-up, power-down and

brownout conditions (see Figure 8 Typical Operating

Circuit).

/RESET changes from high to low whenever the

respective reset threshold voltages, /RESET remains low

for the reset timeout period and than goes high. /RESET

is one-shot pulsed whenever selected manual reset inputs

are asserted. /RESET stays asserted for the normal reset

timeout period (140ms).

/RESET is guaranteed to be in the proper output logic

Manual Reset Input Options

Unlike typical manual reset functions associated with

supervisors, each device in the PT7M7443~ 7452 family

includes at lease one manual reset input, which must be

held logic-low for an extended setup period (6.72 typ)

before the /RESET output asserts. When valid manual reset

input conditions/setup periods are met, the /RESET output

is one-shot pulse asserted low for a fixed reset timeout

period (140ms min). Existing front-panel pushbutton

switches (i.e., power on/off, channel up/down, or mode

select) can be used to drive the manual reset inputs. The

extended manual reset setup period prevents nuisance

system resets during normal front-panel usage or resulting

from inadvertent short-term pushbutton closure.

PT7M7443/7444, PT7M7447/7448, and PT7M7451/7452

include a single manual reset input with extended setup

period (/MR1). The PT7M7445/7446 and PT7M7449/7450

include two manual reset inputs (/MR1 and /MR2) with

extended setup periods. For dual /MR1, /MR2 devices, both

inputs must be held low simultaneously for the extended

setup period (6.72s typ) before the reset output is pulse

asserted. The dual extended setup provides greater protection

from nuisance resets. (For example, the user or service

technician is informed to simultaneously push both the on/off

button and the channel-select button for 6.72s to reset the

system.)

6.72s

MR2

RESET

MR1

210ms