MCP41XXX/42XXX
5.5
Reset (RS) Pin Operation
TABLE 5-1:
TRUTH TABLE FOR LOGIC
INPUTS
The Reset pin (RS) will automatically set all potentiom-
eter data latches to mid-scale (Code 80h) when pulled
low (provided that the pin is held low at least 150 ns
and CS is high). The reset will execute regardless of
the position of the SCK, SHDN and SI pins. It is possi-
ble to toggle RS low and back high while SHDN is low.
In this case, the potentiometer registers will reset to
mid-scale, but the potentiometer will remain in
shutdown mode until the SHDN pin is raised.
SCK CS RS SHDN
Action
X
Ø
H
H
Communication is initiated with
device. Device comes out of
standby mode.
L
L
H
H
No action. Device is waiting for
data to be clocked into shift
register or CS to go high to
execute command.
¦
L
L
H
H
X
X
Shift one bit into shift register.
The shift register can be loaded
while the SHDN pin is low.
Shift one bit out of shift register
on the SO pin. The SO pin is
active while the SHDN pin is
low.
Note:
Bringing the RS pin low while the CS pin is
low constitutes an invalid operating state
and will result in indeterminate results
when RS and/or CS are brought high.
Ø
5.6
Shutdown (SHDN) Pin Operation
When held low, the shutdown pin causes the applica-
tion circuit to go into a power-saving mode by open-cir-
cuiting the A terminal and shorting the B and W
terminals for all potentiometers. Data register contents
are not affected by entering shutdown mode (i.e., when
the SHDN pin is raised, the data register contents are
the same as before the shutdown mode was entered).
X
¦
H
H
Based on command bits, either
load data from shift register into
data latches or execute shut-
down command. Neither com-
mand executed unless
multiples of 16 clocks have
been entered while CS is low.
SO pin goes to a logic low.
While in shutdown mode, it is still possible to clock in
new values for the data registers, as well as toggling
the RS pin to cause all data registers to go to mid-scale.
The new values will take affect when the SHDN pin is
raised.
If the device is powered-up with the SHDN pin held low,
it will power-up in the shutdown mode with the data reg-
isters set to mid-scale.
X
X
H
H
H
Ø
H
H
Static Operation.
All data registers set and
latched to code 80h.
X
X
X
H
H
H
Ø
H
H
L
Ø
¦
All data registers set and
latched to code 80h. Device is
in hardware shutdown mode
and will remain in this mode.
All potentiometers put into
hardware shutdown mode;
terminal A is open and W is
shorted to B.
Note:
Bringing the SHDN pin low while the CS
pin is low constitutes an invalid operating
state and will result in indeterminate
results when SHDN and/or CS are brought
high.
All potentiometers exit hard-
ware shutdown mode. Potenti-
ometers will also exit software
shutdown mode if this rising
edge occurs after a low pulse
on CS. Contents of data
5.7
Power-up Considerations
latches are restored.
When the device is powered on, the data registers will
be set to mid-scale (80h). A power-on reset circuit is
utilized to ensure that the device powers up in this
known state.
2003 Microchip Technology Inc.
DS11195C-page 21
MICROCHIP [ MICROCHIP ]
