DS1868 datasheet(5/14 Pages) DALLAS

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DS1868

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STACKED CONFIGURATION Figure 3

CASCADE OPERATION

A feature of the DS1868 is the ability to control multiple devices from a single processor. Multiple

DS1868s can be linked or daisy chained as shown in Figure 4. As a data bit is entered into the I/O shift

stack select bit of the DS1868 will always be the first out the part at the beginning of a transaction. The

COUT pin will always have the value of the stack select bit (b0) when RST is inactive.

CASCADING MULTIPLE DEVICES Figure 4

The COUT output of the DS1868 can be used to drive the DQ input of another DS1868. When connecting

multiple devices, the total number of bits transmitted is always 17 times the number of DS1868s in the

daisy chain.

An optional feedback resistor can be placed between the COUT terminal of the last device and the first

DS1868 DQ, input thus allowing the controlling processor to read, as well as, write data, or circularly

clock data through the daisy chain. The value of the feedback or isolation resistor should be in the range

from 2 to 10 kohms.

When reading data via the COUT pin and isolation resistor, the DQ line is left floating by the reading

device. When RST is driven high, bit 17 is present on the COUT pin, which is fed back to the input DQ

pin through the isolation resistor. 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 of the next device. After

17 bits (or 17 times the number of DS1868s 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, wiper-1, and stack select bit I/O register.

DS1868 Datasheet(PDF) 5 Page - Dallas Semiconductor