Datasheet
Data Sheet AD9957
Rev. C | Page 57 of 64
Bit (s) Mnemonic Description
21:17 Open
16
Read Effective
FTW
0: a serial I/O port read operation of the FTW register reports the contents of the FTW register (default).
1: a serial I/O port read operation of the FTW register reports the actual 32-bit word appearing at the input to
the DDS phase accumulator.
15:14
I/O Update Rate
Control
Ineffective unless CFR2<23> = 1. Sets the prescale ratio of the divider that clocks the I/O update timer as
follows:
00: divide-by-1 (default).
01: divide-by-2.
10: divide-by-4.
11: divide-by-8.
13
PDCLK Rate
Control
Ineffective unless CFR2<31> = 0 and CFR1<25:24> = 00b.
0: PDCLK operates at the input data rate (default).
1: PDCLK operates at ½ the input data rate; useful for maintaining a consistent relationship between I/Q
words at the parallel data port and the internal clocks of the baseband signal processing chain.
12 Data Format 0: the data-words applied to Pin D<17:0> are expected to be coded as twos complement (default).
1: the data-words applied to Pin D<17:0> are expected to be coded as offset binary.
11 PDCLK Enable
0: the PDCLK pin is disabled and forced to a static Logic 0 state; the internal clock signal continues to operate
and provide timing to the data assembler.
1: the internal PDCLK signal appears at the PDCLK pin (default).
10 PDCLK Invert 0: normal PDCLK polarity; Q-data associated with Logic 1, I-data with Logic 0 (default).
1: inverted PDCLK polarity.
9
TxEnable Invert
0: normal TxENABLE polarity; Logic 0 is standby, Logic 1 is transmit (default).
1: inverted TxENABLE polarity; Logic 0 is transmit, Logic 1 is standby.
8
Q-First Data
Pairing
0: an I/Q data pair is delivered as I-data first, followed by Q-data (default).
1: an I/Q data pair is delivered as Q-data first, followed by I-data.
7 Open
6
Data Assembler
Hold Last Value
Ineffective when CFR1<25:24> = 01b.
0: when the TxENABLE pin is false, the data assembler ignores the input data and internally forces zeros on
the baseband signal path (default).
1: when the TxENABLE pin is false, the data assembler ignores the input data and internally forces the last
value received on the baseband signal path.
5
Sync Timing
Validation Disable
0: enables the setup and hold validation circuit to take a measurement; the measurement result appears at
the SYNC_SMP_ERR pin; a Logic 1 at this pin indicates a potential setup/hold violation whereas a Logic 0
indicates that a setup/hold violation has not been detected; the measurement result is latched and held until
this bit is set to a Logic 1.
1: resets the setup and hold validation measurement circuit forcing the SYNC_SMP_ERR pin to a static Logic 0
condition (default); the measurement circuit is effectively disabled until this bit is restored to a Logic 0 state.
4:0 Open