X9241A
Acknowledge Polling
Instruction Structure
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.
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
Potentiometer
Select
I3
I2
I1
I0
P1
P0
R1
R0
Flow 1. ACK Polling Sequence
Instructions
Register
Select
Nonvolatile Write
Command Completed
Enter ACK Polling
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.
Issue
START
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
Issue Slave
Issue STOP
Address
No
ACK
Returned?
the wiper to this action will be delayed t
. A
Yes
STPWV
transfer from WCR current wiper position, to a Data
Register is a write to nonvolatile memory and takes a
FurTher
OperaTion?
No
minimum of t
to complete. The transfer can occur
WR
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.
Yes
Issue
Instruction
Issue STOP
Proceed
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.
Proceed
Characteristics subject to change without notice. 4 of 18
REV 1.1.13 12/09/02
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