Global Mixed-mode Technology Inc.
G696/G697
Interfacing to µPs with Bidirectional Reset Pins
high as VCC decays toward 0. The voltage where this
occurs depends on the pull-up resistor value and the
voltage to which it is connected.
Since the RESET output on the G697L is open drain,
this device interfaces easily with µPs that have bidirec-
tional reset pins, such as the Motorola 68HC11. Con-
Benefits of Highly Accurate Reset Threshold
Most µP supervisor ICs have reset threshold voltages
between 5% and 10% below the value of nominal
supply voltages. This ensures a reset will not occur
within 5% of the nominal supply, but will occur when
the supply is 10% below nominal.
necting the µP supervisor’s RESET output directly to
the microcontroller’s (µC’s) RESET pin with a single
pull-up resistor allows either device to assert reset
(Figure 5).
G697L Open-Drain RESET Output Allows Use with
Multiple Supplies
When using ICs rated at only the nominal supply ±5%,
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
Generally, the pull-up connected to the G697L will
connect to the supply voltage that is being monitored
at the IC’s VCC pin. However, some systems may use
the open-drain output to level-shift from the monitored
supply to reset circuitry powered by some other supply
(Figure 6). Note that as the G697L’s VCC decreases
below 1V, so does the IC’s ability to sink current at
The G69_ _463/G69_ _308 use highly accurate circuitry
to ensure that reset is asserted close to the 5% limit,
and long before the supply has declined to 10% below
nominal.
RESET . Also, with any pull-up, RESET will be pulled
TEL: 886-3-5788833
http://www.gmt.com.tw
Ver: 1.8
May 10, 2006
9
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
