S9518 Ver la hoja de datos (PDF) - Summit Microelectronics
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Fabricante
S9518
Summit Microelectronics
S9518 Datasheet PDF : 8 Pages
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S9518
DEVICE OPERATION
There are five main blocks to the S9518: an 8-bit EE-
PROM memory; input debounce circuits, control logic,
and 8-bit counter; 8-bit data register; decode section and
resistor ladder (DAC); and the buffer amplifier.
The input control section operates just like an up/down
counter. The output of this counter is fed to the data
register and then decoded to activate one of 255 electronic
switches connected to the resistor ladder. The ladder is
comprised of 256 resistors of equal value connected in
series. At the bottom of the ladder and at the junctions of
the resistors there are electronic switches that transfer the
voltage at each point to the buffer amplifier and then to the
output.
The S9518 is designed to interface directly to two
pushbutton switches that effectively move the potentiom-
eter wiper up or down. The UP# and DWN# inputs,
respectively, increment or decrement the 8-bit counter.
The data input to the DAC is decoded to select one of the
256 wiper positions along the resistive ladder. The wiper
increment input UP# and the wiper decrement input
DWN# are connected to internal pull-ups so that they
normally remain high. When pulled low by an external
pushbutton switch or a logic low level input, the wiper will
be switched to the next adjacent tap position. Internal
debounce circuitry prevents inadvertent switching of the
wiper position if UP# or DWN# remain low for less than
30ms (typical).
Each of the buttons can be pushed either once for a single
increment/decrement or held low continuously for multiple
increments/decrements. The number of increments/dec-
rements of the wiper position depends on how long the
button is pushed. When making a continuous push, after
the first second, the increment/decrement speed in-
creases. For the first second the device will be in the slow
scan mode. Then, if the button is held for longer than one
second, the device will go into the fast scan mode. As soon
as the button is released the S9518 will return to a standby
condition.
The DAC, whether set to 00HEX or FFHEX, acts like its
mechanical equivalent and does not move beyond the last
position. That is, the counter does not wrap around when
clocked up to FFHEX or down to 00HEX.
AUTOSTORE
The value of the counter is stored in EEPROM memory
whenever the chip senses a power-down of VDD while
STR# is enabled (held low). When power is restored the
contents of the memory are recalled and the counter reset
to the last value stored. If AUTOSTORE is to be imple-
mented, STR# is typically hard wired to GND. If STR# is
held high during power-up and then taken low the wiper will
not respond to the UP# or DWN# inputs until STR# is
brought high and the store is complete. See Figure 1.
Manual (Pushbutton) Store
When STR# is not enabled (held high) a pushbutton switch
may be used to pull STR# low and released to perform a
manual store of the wiper position in EEPROM memory.
See Figure 2.
Effect of VDD Removal
The resistor ladder, connected between VH and VL, does
not change value when VDD is removed. However, the
buffer amplifier no longer functions, and consequently a
high impedance appears at the VOUT pin.
VDD
470Ω
1
2
3
4
UP#
DWN#
VH
GND
VDD
STR#
VL
VOUT
8
7
6
5
22µF
VDD
1
2
3
4
UP#
DWN#
VH
GND
VDD
STR#
VL
VOUT
8
7
6
5
20kΩ
2017 T Fig01 5.1
Figure 1: Typical circuit with STR store pin used in
AUTOSTORE mode
2017 T Fig02 5.0
Figure 2: Typical circuit with STR store pin
controlled by push button switch
SUMMIT MICROELECTRONICS, Inc.
2017 5.2 8/2/00
3
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