I would like to be able to "freeze" the value in the conversion register while in Mode 2 using a signal local to the AD7992. Will holding ^CONVST high prevent the start of conversion that would be initiated by an I2C write command (or at least block the update of the conversion register)? If so, is there any downside to this approach, other than that the converter is powered up while ^CONVST is high? Can the conversion register be read while ^CONVST is high?
I'm currently looking into this. I'll send you update as soon as possible.
In initiating Modes2 and Mode3, CONVST pin should be tied to low else we are initiating Mode1. In Mode1 CONVST signal must remain high for 1us for the part to fully power up. The failing edge of CONVST signal places the track and hold and conversion also takes place. It is recommended that the I2C bus is quiet when a conversion is taking place.
We cannot guarantee a correct data conversion for that case. The mode of operation in the datasheet for CONVST pin should be tied low for all other modes of operation.
I guess my original question wasn't sufficiently clear. If the 7992 is running in Mode 2, with a conversion is in progress, and the ^CONVST line is raised, what will happen? Will a conversion in progress be completed? What will be left in the conversion register, and will it be readable while ^CONVST is held HIGH? Will the conversion register content remain stable until ^CONVST is lowered again?