DS1667

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CLK input. Data input on the DQ pin can be changed while the clock input is high or low, but only data

meeting the setup requirements will enter the shift register. Data is always entered starting with the value

of the stack select bit. The next 8 bits to be entered are those specifying the wiper 1 setting. The MSB of

these 8 bits is sent first. The next 8 bits to be entered are those specifying the wiper 0 setting, sent MSB

first. The 17

than 17 bits are entered, the value of the potentiometer settings will result from the number of bits that

were entered plus the remaining bits of the old value shifted over by the number of bits sent. If more than

17 bits are sent, only the last 17 bits are left in the shift register. Therefore, sending other than 17 bits can

produce indeterminate potentiometer settings.

As bits are entered into the shift register, the previous value is shifted out bit by bit on the cascade serial

port pin (COUT). By connecting the COUT pin to the DQ pin of a second DS1667, multiple devices can

be daisy chained together as shown in Figure 3.

When connecting multiple devices, the total number of bits sent is always 17 times the number of

DS1667s in the daisy chain. In applications where it is desirable to read the settings of potentiometers, the

COUT pin of the last device connected in a daisy chain must be connected back to the DQ input of the

first device through a resistor with a value of 1k to 10k. This resistor provides isolation between COUT

and DQ when writing to the device (see Figure 3).

always present on the COUT pin, which is fed back to the input DQ pin through the resistor (see Figure

data transfer. When the CLK input transitions low to high, bit 17 is loaded into the first position of the

I/O shift register and bit 16 becomes present on COUT and DQ. After 17 bits (or 17 times the number of

devices for a daisy chain), the data has shifted completely around and back to its original position. When

RST

is transitioned back low to end data transfer, the value (the same as before the read occurred) is

loaded into the wiper 0 and wiper 1 registers and the stack select bit.

When power is applied to the DS1667, the device always has the wiper settings at half position and the

stack select bit is at 0.