DS2890

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Figure 11. 1-WIRE CRC GENERATOR

R

8TH

STAGE

7TH

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6TH

STAGE

5TH

STAGE

4TH

STAGE

3RD

STAGE

2ND

STAGE

1ST

STAGE

S

INPUT DATA

POTENTIOMETER FUNCTION COMMANDS

Once the bus master has completed a ROM command sequence, one of six DS2890 potentiometer

function commands can be issued. The Potentiometer Function Command flow charts, Figure 16 and

Figure 17, describe the protocols necessary for adjusting or reading the potentiometer wiper position or

controlling the operating state of the DS2890. All potentiometer functions consist of a single command

byte followed by one or more bytes of data or control written/read by the bus master. All data transferred

between the DS2890 and the bus master are communicated least significant bit first.

READ POSITION [F0H]

The Read Position command is used to obtain the wiper setting of the potentiometer currently addressed

by the Control Register. Although the DS2890 is a single element potentiometer, wiper addressing still

applies and the Control Register wiper number used for addressing must be set accordingly. In addition

to wiper position, the Control Register byte will be returned with a Read Position command. This enables

the bus master to easily confirm/determine the currently addressed potentiometer wiper. Following the

Read Position command byte, the bus master reads 16 bits to obtain first the Control Register byte then

the wiper position byte. The DS2890 will respond with 0’s to additional reads after the 8 bit of the

position byte. The Read Position command is terminated with a Reset pulse.

WRITE POSITION [0FH]

The Write Position command is used to set the position of the currently addressed potentiometer wiper.

Although the DS2890 is a single element potentiometer, wiper addressing still applies and the Control

Register wiper number used for addressing must be set accordingly. The bus master follows the Write

Position command byte with an 8-bit wiper position value. Following the 8th bit of the position byte, the

bus master reads back the 8-bit position value from the DS2890 to confirm that the value was received

correctly by the device. If an incorrect value is read back, the bus master must issue a Reset pulse and

repeat the sequence. If the value read back is correct, the bus master then sends the 8-bit release code

(96h). If the DS2890 accurately receives the release code, the wiper position is updated and the device

will respond with 0’s to additional reads by the bus master. If an invalid release code is received, no

change is made to the wiper position and the device will respond with 1’s to additional reads by the bus

master. The Write Position command is terminated with a Reset pulse.