X9241A

Characteristics subject to change without notice.

4 of 18

REV 1.1.13 12/09/02

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Acknowledge Polling

The disabling of the inputs, during the internal

nonvolatile write operation, can be used to take

advantage of the typical 5ms EEPROM write cycle

time. Once the stop condition is issued to indicate the

end of the nonvolatile write command the X9241A

initiates the internal write cycle. ACK polling can be

initiated immediately. This involves issuing the start

condition followed by the device slave address. If the

X9241A is still busy with the write operation no ACK

will be returned. If the X9241A has completed the

write operation an ACK will be returned and the

master can then proceed with the next operation.

Flow 1. ACK Polling Sequence

Instruction Structure

The next byte sent to the X9241A contains the

instruction and register pointer information. The four

most significant bits are the instruction. The next four

bits point to one of four pots and when applicable they

point to one of four associated registers. The format is

shown below in Figure 2.

Figure 2. Instruction Byte Format

The four high order bits define the instruction. The next

two bits (P1 and P0) select which one of the four

potentiometers is to be affected by the instruction. The

last two bits (R1 and R0) select one of the four

registers that is to be acted upon when a register

oriented instruction is issued.

Four of the nine instructions end with the transmission

of the instruction byte. The basic sequence is

illustrated in Figure 3. These two-byte instructions

exchange data between the WCR and one of the data

registers. A transfer from a Data Register to a WCR is

essentially a write to a static RAM. The response of

transfer from WCR current wiper position, to a Data

Register is a write to nonvolatile memory and takes a

between one of the four potentiometers and one of its

associated registers; or it may occur globally, wherein

the

transfer

occurs

between

all

four

of

the

potentiometers and one of their associated registers.

Four instructions require a three-byte sequence to

complete. These instructions transfer data between

the host and the X9241A; either between the host and

one of the Data Registers or directly between the host

and the WCR. These instructions are: Read WCR,

read the current wiper position of the selected pot;

Write WCR, change current wiper position of the

selected pot; Read Data Register, read the contents of

the selected nonvolatile register; Write Data Register,

write a new value to the selected Data Register. The

sequence of operations is shown in Figure 4.

Nonvolatile Write

Command Completed

Enter ACK Polling

Issue

START

Issue Slave

Address

ACK

Returned?

FurTher

OperaTion?

Issue

Instruction

Proceed

Issue STOP

No

Yes

Yes

Proceed

Issue STOP

No

I1

I2

I3

I0

P1

P0

R1

R0

Potentiometer

Select

Register

Select

Instructions