Datasheet

AD9553
Rev. A | Page 39 of 44
REFB Frequency Control (Register 0x23 to Register 0x26)
Table 35.
Address Bit Bit Name Description
0x23 [7:0] REFB divider (R
B
) Bits[13:6] of the 14-bit REFB divider.
0x24 [7:2] REFB divider (R
B
) Bits[5:0] of the 14-bit REFB divider (default: R
B
= 8192 decimal). The REFB divider bits
are ineffective unless Register 0x24[1] = 1.
1 Enable SPI control of R
B
Enables SPI port control of the REFB divider value (R
B
).
0 = the A3 to A0 pins define R
B
per Table 14 (default).
1 = the 14-bit value in the REFB divider register defines R
B
.
0 Unused Unused.
0x25 7 Enable SPI control of ×2
B
Enables SPI control of the REFB ×2 frequency multiplier (×2
B
) per Register 0x25[6].
0 = the device automatically selects ×2
B
per Table 14 (default).
1 = Register 0x25[6] controls the selection of ×2
B
.
6 Select ×2
B
Selects ×2
B
. This bit is ineffective unless Register 0x25[7] = 1.
0 = bypass ×2
B
(default).
1 = select ×2
B
.
5 Enable SPI control of ÷5
B
Enables SPI control of the ÷5
B
prescaler per Register 0x25[4].
0 = the device automatically selects ÷5
B
per Table 14 (default).
1 = Register 0x25[4] controls the selection of ÷5
B
.
4 Select ÷5
B
Selects ÷5
B
. This bit is ineffective unless Register 0x25[5] = 1.
0 = bypass ÷5
B
(default).
1 = select ÷5
B
.
[3:0] Unused Unused.
0x26 [7:0] Unused Unused.
DCXO Frequency and Reference Switchover Control (Register 0x27 to Register 0x31)
Table 36.
Address Bit Bit Name Description
0x27 [7:0] XO divider (R
XO
) Bits[13:6] of the 14-bit XO divider.
0x28 [7:2] XO divider (R
XO
) Bits[5:0] of the 14-bit XO divider (default: R
XO
= 4096 decimal). The XO divider bits are
ineffective unless Register 0x28[1] = 1.
1 Enable SPI control of R
XO
Enables SPI port control of the XO divider value (R
XO
).
0 = the A3 to A0 pins define R
XO
per Table 14 (default).
1 = the 14-bit value in the XO divider register defines R
XO
.
0 Unused Unused.
0x29 [7:6] Switchover mode Selects the switchover operating mode.
00 = revertive switchover (default).
01 = nonrevertive switchover.
10 = selects REFA as the active reference.
11 = selects REFB as the active reference.
5 REFA diff Enables the differential input reference function.
0 = normal single-ended operation of REFA and REFB (default).
1 =
REFA configured as a differential reference in which the REFA pin functions as one
differential input and the REFB/
REFA
pin functions as the other differential input. In this
configuration, the REFB channel and switchover functionality are both unavailable.
[4:0] Unused Unused.
0x2A to
0x31
[7:0] Unused Unused.