X9428
Acknowledge Polling
Figure 2. Instruction Byte Format
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 X9428
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
X9428 is still busy with the write operation no ACK will
be returned. If the X9428 has completed the write
operation an ACK will be returned, and the master can
then proceed with the next operation.
Register
Select
I3
I2
I1
I0
R1 R0
0
0
Instructions
The four high order bits define the instruction. The next
two bits (R1 and R0) select one of the four registers that
is to be acted upon when a register oriented instruction
is issued. Bits 0 and 1 are defined to be 0.
Flow 1. ACK Polling Sequence
Four of the seven 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 Wiper Counter Register and one of the
Data Registers. A transfer from a Data Register to a
Wiper Counter Register is essentially a write to a static
RAM. The response of the wiper to this action will be
Nonvolatile Write
Command Completed
Enter ACK Polling
Issue
START
delayed t
. A transfer from the Wiper Counter
WRL
Register (current wiper position), to a Data Register is a
write to nonvolatile memory and takes a minimum of
t
to complete.
Issue Slave
Issue STOP
Address
WR
Four instructions require a three-byte sequence to
complete. These instructions transfer data between the
host and the X9428; either between the host and one of
the Data Registers or directly between the host and the
Wiper Counter Register. These instructions are: Read
Wiper Counter Register (read the current wiper position
of the selected pot), write Wiper Counter Register
(change current wiper position of the selected pot), read
Data Register (read the contents of the selected
nonvolatile register) and write Data Register (write a
new value to the selected Data Register). The
sequence of operations is shown in Figure 4.
ACK
Returned?
NO
YES
NO
Further
Operation?
YES
Issue
Instruction
Issue STOP
Proceed
Proceed
Instruction Structure
The next byte sent to the X9428 contains the instruction
and register pointer information. The four most
significant bits are the instruction. The next four bits
point to one of four associated registers. The format is
shown below in Figure 2.
FN8197.1
April 26, 2006
6
INTERSIL [ Intersil ]
