DS1800 Datasheet, PDF (6/14 Pages) Dallas Semiconductor – Dual Inverting Log Gain/Attenuator

DS1800
MUTE CONTROL
The DS1800 provides a mute control feature which can be accessed by the user through hardware or
software. Hardware control of the device is achieved through the MUTE input pin. This pin is internally
pulled up through a 50 kΩ resistor and functions like the PxG and PxA pushbutton controls. When this
input is driven low, the wiper outputs of both potentiometers will be internally connected to the OUTx
terminal of their respective potentiometers. This input performs as a toggle input, with the first activity
on this pin connecting the wiper terminals to the OUTx terminals (position 128) of the potentiometer.
The next input activity on this pin will return the wiper position to the previous state before muting
occurred.
Also, if operating in pushbutton mode, MUTE will be deactivated if an input is received over any push–
button input. This input, like the pushbutton inputs, is internally debounced and requires no external
circuitry. When the device powers up, the first activity on the mute pin will move the wipers to position
128 or the OUTx end of the potentiometer(s).
Software muting was discussed in the 3–wire serial control section. Bits 7 and 15 are reserved for muting
each respective potentiometer. If these bits have value 1, the wiper positions of the pot will be transferred
to the mute position. Unlike hardware mute control, software muting allows the user individual control of
each potentiometer. Additionally, the software mute requires that the complete wiper position setting be
rewritten to establish a non-muted position. Note that bits 7 and 15 of the I/O shift register must have
value 0 to release the software mute position.
CASCADE OPERATION
A feature of the DS1800 is the ability to control multiple devices from a single processor. Multiple
DS1800’s can be linked or daisy-chained as shown in Figure 8. As a data bit is entered into the I/O shift
register of the DS1800, a data bit will appear at the C_OUT output after a maximum delay of 50
nanoseconds.
The C_OUT output of the DS1800 can be used to drive the D input of another DS1800. When connecting
multiple devices, the total number of bits sent is always 16 times the number of DS1800’s is the daisy
chain.
An optional feedback resistor can be placed between the C_OUT terminal of the last device and the D input
of the first DS1800, thus allowing the controlling processor to circularly clock data through the daisy
chain. The value of the feedback or isolation resistor should be in the range from 2 kΩ=to 20 kΩ.
When reading data via the C_OUT pin and the isolation resistor, the D input is left floating by the reading
device. When RST is driven high, bit 0 is present on the C_OUT pin, which is fed back to the D pin through
the isolation resistor. When the CLK input transitions low to high, bit 0 is loaded into the first position of
the I/O shift register and bit 1 becomes present on C_OUT and D of the next device. After 16 bits (or 16
times the number of DS1800s in the daisy chain), the data has shifted completely around and back to its
original position. When RST transitions to the low state to end data transfer, the value (the same as before
the read occurred is loaded into the wiper–0 and wiper–1 registers.
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