X9110_08 Datasheet, PDF (6/18 Pages) Intersil Corporation – Dual Supply/Low Power/1024-Tap/SPI Bus

X9110
TABLE 4. IDENTIFICATION BYTE FORMAT
DEVICE TYPE
IDENTIFIER
ID3
ID2
ID1
ID0
0
1
0
1
(MSB)
TABLE 5. INSTRUCTION BYTE FORMAT
INSTRUCTION
OPCODE
0
0
REGISTER
SELECTION
INTERNAL SLAVE
ADDRESS
READ OR
WRITE BIT
A0
R/W
(LSB)
I2
I1
I0
0
(MSB)
Device Instructions
Identification Byte (ID and A)
The first byte sent to the X9110 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 X9110;
this is fixed as 0101[B] (refer to Table 4).
The A0 bit in the ID byte is the internal slave address. The
physical device address is defined by the state of the A0 input
pin. The slave address is externally specified by the user. The
X9110 compares the serial data stream with the address input
state; a successful compare of the address bit is required for
the X9110 to successfully continue the command sequence.
Only the device whose slave address matches the incoming
device address sent by the master executes the instruction.
The A0 input can be actively driven by CMOS input signals or
tied to V_CC or V_SS. The R/W bit is used to set the device to
either read or write mode.
Instruction Byte and Register Selection
The next byte sent to the X9110 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 registers. The format is
shown in Table 5.
Five of the seven instructions are four bytes in length. 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
data register
RB
RA
0
RB
RA REGISTER
0
0
0
1
1
0
1
1
DR0
DR1
DR2
DR3
0
(LSB)
• Write Data Register – write a new value to the selected
data register
• Read Status – This command returns the contents of the
WIP bit which indicates if the internal write cycle is in
progress
The basic sequence of the four byte instructions is illustrated
in Figure 3. These four-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, with the static RAM controlling the wiper
position. The response of the wiper to this action will be
delayed by t_WRL. A transfer from the WCR (current wiper
position), to a Data Register is a write to nonvolatile memory
and takes a minimum of t_WR to complete. The transfer can
occur between the potentiometer and one of its associated
registers. The Read Status Register instruction is the only
unique format (see Figure 4).
Two instructions require a two-byte sequence to complete
(See Figure 2). These instructions transfer data between the
host and the X9110; either between the host and one of the
Data Registers or directly between the host and the Wiper
Counter Register. These instructions are:
• XFR Data Register to Wiper Counter Register – This
transfers the contents of one specified Data Register to
the associated Wiper Counter Register
• XFR Wiper Counter Register to Data Register – This
transfers the contents of the specified Wiper Counter
Register to the specified associated Data Register
See Instruction format for more details.
6
FN8158.3
February 13, 2008