Datasheet

AD5291/AD5292
Rev. D | Page 24 of 32
BASIC OPERATION
The basic mode of setting the variable resistor wiper position
(programming the RDAC register) is accomplished by loading
the shift register with Command 1 (see Table 11) and the desired
wiper position data. When the desired wiper position is deter-
mined, the user can load the shift register with Command 3
(see Tabl e 11), which stores the wiper position data in the 20-TP
memory register. After 6 ms, the wiper position is permanently
stored in the 20-TP memory. The RDY pin can be used to moni-
tor the completion of this 20-TP program. Table 12 provides a
programming example, listing the sequence of serial data input
(DIN) words with the serial data output appearing at the SDO
pin in hexadecimal format.
20-TP READBACK AND SPARE MEMORY STATUS
It is possible to read back the contents of any of the 20-TP
memory registers through SDO by using Command 5 (see
Table 1 1). The lower five LSB bits (D0 to D4) of the data byte
select which memory location is to be read back (see Table 16).
Data from the selected memory location are clocked out of the
SDO pin during the next SPI operation, where the last 10 bits
contain the contents of the specified memory location.
It is also possible to calculate the address of the most recently
programmed memory location by reading back the contents of
read-only Memory Address 0x14 and Memory Address 0x15
using Command 5. The data bytes read back from Memory
Address 0x014 and Memory Address 0x015 are thermometer
encoded versions of the address of the last programmed
memory location.
For the example outlined in Table 15, the address of the last
programmed location is calculated as
(Number of Bits = 1 in Memory Address 0x14) + (Number
of Bits = 1 in Memory Address 0x15) − 1 = 10 + 8 − 1 = 17
(0x10)
If no memory location has been programmed, then the address
generated is −1.
SHUTDOWN MODE
The AD5291 and AD5292 can be placed in shutdown mode by
executing the software shutdown command, Command 8 (see
Table 1 1), and setting the LSB, D0, to 1. This feature places the
RDAC in a special state in which Terminal A is open-circuited,
and Wiper W is connected to Terminal B. The contents of the
RDAC register are unchanged by entering shutdown mode.
However, all commands listed in Table 11 are supported while
in shutdown mode. Execute Command 8 (see Table 1 1 ), and set
the LSB, D0, to 0 to exit shutdown mode.
Table 15. Example 20-TP Memory Readback
DIN SDO Action
0x1414 0xXXXX Prepares data read from Memory Address 0x14.
0x1415 0x03FF
Prepares data read from Memory Address 0x15. Sends 16-bit word out of SDO, where the last 10 bits contain the
contents of Memory Address 0x14.
0x0000 0x00FF NOP Command 0 sends 16-bit word out of SDO, where last 10-bits contain the contents of Memory Address 0x15.
0x1410 0x0000 Prepares data read from memory location 0x10.
0x0000 0xXXXX NOP Instruction 0 sends 16-bit word out of SDO, where the last 10 bits contain the contents of Memory Address 0x10 (17).
Table 16. Memory Map of Command 5
Data Bits [DB9:DB0]
1
D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Register Contents
X X X X X 0 0 0 0 0 1
st
programmed wiper location (0x00)
X X X X X 0 0 0 0 1 2
nd
programmed wiper location (0x01)
X X X X X 0 0 0 1 0 3
rd
programmed wiper location (0x02)
X X X X X 0 0 0 1 1 4
th
programmed wiper location (0x03)
X X X X X 0 0 1 0 0 5
th
programmed wiper location (0x04)
… … … … … … … … … … …
X X X X X 0 1 0 0 1 10
th
programmed wiper location (0x09)
X X X X X 0 1 1 1 0 15
th
programmed wiper location (0x0E)
X X X X X 1 0 0 1 1 20
th
programmed wiper location (0x13)
X X X X X 1 0 1 0 0 Programmed memory status (thermometer encoded)
2
(0x14)
X X X X X 1 0 1 0 1 Programmed memory status (thermometer encoded)
2
(0x15)
1
X = don’t care.
2
Allows the user to calculate the remaining spare memory locations.