X9279 Datasheet, PDF (7/22 Pages) Xicor Inc. – Single Digitally-Controlled (XDCP) Potentiometer

X9279
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 X9279
initiates the internal write cycle. ACK polling, Flow 1,
can be initiated immediately. This involves issuing the
start condition followed by the device slave address. If
the X9279 is still busy with the write operation no ACK
will be returned. If the X9279 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
Nonvolatile Write
Command Completed
EnterACK Polling
Issue
START
Issue Slave
Address
Issue STOP
ACK
No
Returned?
Yes
Further
No
Operation?
Yes
Issue
Instruction
Issue STOP
Proceed
Proceed
INSTRUCTION AND REGISTER DESCRIPTION
Device Addressing: Identification Byte ( ID and A)
The first byte sent to the X9279 from the host,
following a CS going HIGH to LOW, is called the
Identification byte. The most significant four bits of the
slave address are a device type identifier. The ID[3:0]
bits is the device ID for the X9279; this is fixed as
0101[B] (refer to Table 1).
The A[2:0] bits in the ID byte is the internal slave
address. The physical device address is defined by
the state of the A2 - A0 input pins. The slave address
is externally specified by the user. The X9279
compares the serial data stream with the address
input state; a successful compare of both address bits
is required for the X9279 to successfully continue the
command sequence. Only the device which slave
address matches the incoming device address sent by
the master executes the instruction. The A2 - A0
inputs can be actively driven by CMOS input signals or
tied to V_CC or V_SS.
Instruction Byte (I)
The next byte sent to the X9279 contains the
instruction and register pointer information. The three
most significant bits are used provide the instruction
opcode I [2:0]. The RB and RA bits point to one of the
four Data Registers. P0 is the POT selection; since the
X9279 is single POT, the P0 = 0. The format is shown
in Table 2.
Register Bank Selection (RB, RA, P1, P0)
There are 16 registers organized into four banks. Bank
0 is the default bank of registers. Only Bank 0 registers
can be used for Data Register to Wiper Counter
Register operations.
Banks 1, 2, and 3 are additional banks of registers (12
total) that can be used for 2-Wire write and read
operations. The Data Registers in Banks 1, 2, and 3
cannot be used for direct read/write operations
between the Wiper Counter Register.
7
FN8175.2
September 27, 2005