X9455 Datasheet, PDF (11/18 Pages) Intersil Corporation – Dual Two-wiper Digitally-Controlled (XDCP) Potentiometer

X9455
Slave Address Byte
Following a START condition, the master must output a
Slave Address Byte (Refer to figure 4.). This byte includes
three parts:
• The four MSBs (SA7-SA4) are the Device Type Identifier,
which must always be set to 0101 in order to select the
X9455.
• The next three bits (SA3-SA1) are the Device Address bits
(AS2-AS0). To access any part of the X9455’s memory,
the value of bits AS2, AS1, and AS0 must correspond to
the logic levels at pins A2, A1, and A0 respectively.
• The LSB (SA0) is the R/W bit. This bit defines the
operation to be performed on the device being addressed.
When the R/W bit is “1”, then a Read operation is
selected. A “0” selects a Write operation.
SA7 SA6 SA5 SA4 SA3 SA2 _{SA1 SA0}
0
1
0
1 AS2 AS1 AS0 R/W
Device Type
Identifier
Device
Address
Read or
Write
SLAVE ADDRESS
BIT(S)
DESCRIPTION
SA7-SA4
Device Type Identifier
SA3-SA1
Device Address
SA0
Read or Write Operation Select
FIGURE 4. SLAVE ADDRESS (SA) FORMAT
Nonvolatile Write Acknowledge Polling
After a nonvolatile write command sequence is correctly
issued (including the final STOP condition), the X9455
initiates an internal high voltage write cycle. This cycle
typically requires 5 ms. During this time, any Read or Write
command is ignored by the X9455. Write Acknowledge
Polling is used to determine whether a high voltage write
cycle is completed.
During acknowledge polling, the master first issues a START
condition followed by a Slave Address Byte. The Slave
Address Byte contains the X9455’s Device Type Identifier
and Device Address. The LSB of the Slave Address (R/W)
can be set to either 1 or 0 in this case. If the device is busy
within the high voltage cycle, then no ACK is returned. If the
high voltage cycle is completed, an ACK is returned and the
master can then proceed with a new Read or Write
operation. (Refer to figure 5.)
Byte load completed by issuing
STOP. Enter ACK Polling
Issue START
Issue Slave Address
Byte (Read or Write)
Issue STOP
NO
ACK returned?
YES
High Voltage
complete. Continue command
sequence.
YES
Continue normal Read or Write
command sequence
NO
Issue STOP
PROCEED
FIGURE 5. ACKNOWLEDGE POLLING SEQUENCE
2-Wire Serial Interface Operation
X9455 Digital Potentiometer Register Organization
Refer to the Functional Diagram on page 1. There are 2
Digital Potentiometers, referred to as DCP0, and DCP1.
Each potentiometer has two volatile Wiper Control Registers
(WCRs). Each wiper has four non-volatile registers to store
wiper position or general data. See Table 2 for register
numbering.
11
FN8202.0
November 10, 2004