Datasheet

AD5174
Rev. B | Page 15 of 20
Table 10. Memory Map
Data Byte[DB9:DB0]
1
Command Number
D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Register Contents
X X X 0 0 0 0 0 0 0 Reserved
X X X 0 0 0 0 0 0 1 1
st
programmed wiper location (0x01)
X X X 0 0 0 0 0 1 0 2
nd
programmed wiper location (0x02)
X X X 0 0 0 0 0 1 1 3
rd
programmed wiper location (0x03)
X X X 0 0 0 0 1 0 0 4
th
programmed wiper location (0x04)
… … … … … … … … … … …
X X X 0 0 0 1 0 1 0 10
th
programmed wiper location (0xA)
… … … … … … … … … … …
X X X 0 0 1 0 1 0 0 20
th
programmed wiper location (0x14)
… … … … … … … … … … …
X X X 0 0 1 1 1 1 0 30
th
programmed wiper location (0x1E)
… … … … … … … … … … …
X X X 0 1 0 1 0 0 0 40
th
programmed wiper location (0x28)
… … … … … … … … … … …
X X X 0 1 1 0 0 1 0 50
th
programmed wiper location (0x32)
… … … … … … … … … … …
X X X 0 1 1 1 0 0 1 MSB resistance tolerance (0x39)
5
X X X 0 1 1 1 0 1 0 LSB resistance tolerance (0x3A)
1
X is don’t care.
SDO PIN AND DAISY-CHAIN OPERATION
The serial data output pin (SDO) serves two purposes: it can be
used to read the contents of the wiper setting and 50-TP values
using Command 2 and Command 5, respectively (see Table 6)
or the SDO pin can be used in daisy-chain mode. Data is
clocked out of SDO on the rising edge of SCLK. The SDO pin
contains an open-drain N-channel FET that requires a pull-up
resistor. To place the pin in high impedance and minimize the
power dissipation when the pin is used, the 0x8001 data word
followed by Command 0 should be sent to the part. Table 11
provides a sample listing for the sequence of the serial data
input (DIN). Daisy chaining minimizes the number of port pins
required from the controlling IC. As shown in Figure 26, users
need to tie the SDO pin of one package to the DIN pin of the
next package. Users may need to increase the clock period,
because the pull-up resistor and the capacitive loading at the
SDO-to-DIN interface may require additional time delay
between subsequent devices. When two AD5174 devices are
daisy-chained, 32 bits of data are required. The first 16 bits go to
U2, and the second 16 bits go to U1.
Table 11. Minimize Power Dissipation at SDO Pin
DIN SDO
1
Action
0xXXXX 0xXXXX Last user command sent to the digipot
0x8001 0xXXXX
Prepares the SDO pin to be placed in
high impedance mode
0x0000
High
Impedance
The SDO pin is placed in high
impedance
1
X is don’t care.
Keep the
SYNC
pin low until all 32 bits are clocked into their
respective serial registers. The
SYNC
pin is then pulled high to
complete the operation.
DINMOSI
SSSCLK
SDO
SCLK
DIN SDO
AD5174
U1
AD5174
U2
SYNC
SCLK
SYNC
V
DD
µC
R
P
2.2kΩ
08718-006
Figure 26. Daisy-Chain Configuration Using SDO