Datasheet

Data Sheet AD5291/AD5292
THEORY OF OPERATION
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WRITE PROTECTION
On power-up, the shift register write commands for both the RDAC
register and the 20-TP memory register are disabled. The RDAC
write protect bit, C1 of the control register (see Table 12 and Table
13), is set to 0 by default. This disables any change of the RDAC
register content regardless of the software commands, except that
the RDAC register can be refreshed from the 20-TP memory using
the software reset command (Command 4) or through hardware
by the RESET pin. To enable programming of the variable resistor
wiper position (programming the RDAC register), the write protect
bit, C1 of the control register, must first be programmed. This is
accomplished by loading the shift register with Command 6 (see
Table 11). To enable programming of the 20-TP memory block bit,
C0 of the control register (set to 0 by default) must first be set to 1.
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 determined, the
user can load the shift register with Command 3 (see Table 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 monitor the completion of this
20-TP program. Table 14 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 11). The
lower five LSB bits (D0 to D4) of the data byte select which memory
location is to be read back (see Table 15). 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 ver-
sions of the address of the last programmed memory location.
For the example outlined in Table 16, 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.
Table 16. 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).