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ENABLE EXTERNAL MODULATION (WRITE ONLY)
If this bit is set to 0, the values in bits 25 through 22 (Synthesizer A Profile Select and Synthesizer B
Profile Select respectively) will control the selection of frequency/phase profiles for the synthesizers,
regardless of the state of the External modulation inputs.
If this bit is set to 1, the TTL signals (synchronized to the on-board 125 MHz clock) on MOD_A and
MOD_B will control the selection of frequency/phase profiles for the synthesizers, in the manner
consistent with the setting of the External Modulation Mode bit described above.
READ_SYNTH_SELECT (WRITE ONLY)
This bit is currently not supported.
ARM_WRITE (WRITE ONLY)
When this bit is set to 1 (and the Ext_Mod bit is set to 1) upon a transition on either of the TTL input
signals, the CPLD will write to both DDSs as follows:
Trig/Mod B (TTL input) Low -> High transition: CPLD writes 0x80 to address 0x01
Trig/Mod B (TTL input) High -> Low transition: CPLD writes 0x00 to address 0x01
Trig/Mod A (TTL input) Low -> High transition: CPLD writes 0xC0 to address 0x02
Trig/Mod A (TTL input) High -> Low transition: CPLD writes 0x00 to address 0x02
Writes to the two addresses, if any, are accomplished on opposite edges of the PCI clock to avoid
data/address conflict.
EXTERNAL_CLK (WRITE ONLY)
For board models in which an external clock input is available, when this bit is set to 1, the board will
use the externally supplied clock. When this bit is set to 0 the board will use the on board 1GHz clock.
On Model Synth300-TRIG-HS and Synth300-TRIG-TTL, the External_clk bit must never
be programmed to 1.
WRITE IS TO SYNTH B, WRITE IS TO SYNTH A (WRITE ONLY)
When the Write is to Synth B bit is a 1, then the Sample IC Data Word specified below will be written to
synthesizer B. When the Write is to Synth A bit is a 1, then the Sample IC Data Word specified below
will be written to synthesizer A. When both of these two bits are high, then the data will be written
simultaneously to both synthesizer ICs. In any of these cases, the data in Sample IC Data Word will
be written to the register specified by Synthesizer IC Register Address (discussed below). If both of
these bits are 0, the data will not be written to either synthesizer.
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