9

FN8164.5

December 14, 2006

Cascade Mode

The X9241A provides a mechanism for cascading the

arrays. That is, the sixty-three resistor elements of one array

may be cascaded (linked) with the resistor elements of an

Figure 9).

Cascade Control Bits

The data byte, for the three-byte commands, contains 6 bits

(LSBs) for defining the wiper position plus two high order

bits, CM (Cascade Mode) and DW (Disable Wiper, normal

operation).

The state of the CM bit (bit 7 of WCR) enables or disables

cascade mode. When the CM bit of the WCR is set to “0” the

potentiometer is in the normal operation mode. When the

CM bit of the WCR is set to “1” the potentiometer is

cascaded with its adjacent higher order potentiometer. For

example; if bit 7 of WCR2 is set to “1”, pot 2 will be cascaded

to pot 3.

The state of DW enables or disables the wiper. When the

DW bit (bit 6 of the WCR) is set to “0” the wiper is enabled;

when set to “1” the wiper is disabled. If the wiper is disabled,

the wiper terminal will be electrically isolated and float.

wiper terminals of the cascaded arrays must be electrically

connected externally. All but one of the wipers must be

disabled. The user can alter the wiper position by writing

directly to the WCR or indirectly by transferring the contents

of the Data Registers to the WCR or by using the

Increment/Decrement command.

When using the Increment/Decrement command the wiper

position will automatically transition between arrays. The

current position of the wiper can be determined by reading

the WCR registers; if the DW bit is “0”, the wiper in that array

is active. If the current wiper position is to be maintained on

power-down a global XFR WCR to Data Register command

must be issued to store the position in NV memory before

power-down.

It is possible to connect three or all four potentiometers in

cascade mode. It is also possible to connect POT 3 to POT 0

as a cascade. The requirements for external connections of

Pot 0

WCR0

Pot 1

WCR1

Pot 2

WCR2

Pot 3

WCR3

External

Connection

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FIGURE 9. CASCADING ARRAYS

X9241A