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AD9914 and IO_UPDATE

Question asked by MikeHolt on Sep 28, 2015
Latest reply on Oct 15, 2015 by KennyG

Hello everyone!

I need to ask two things concerning IO_UPDATE.

  1. Edge sensitive or active high and consequences: In the datasheet, it reads:
  • (Table 2. AC SPECIFICATIONS) IO_UPDATE Pin Setup Time to SYNC_CLK: 2ns, IO_UPDATE Pin Hold Time to SYNC_CLK: 0ns.
  • (Table 5. Pin Function Descriptions)  I/O_UPDATE Input/Output Update. Digital input (active high). A high on this pin transfers the contents of the I/O buffers to the corresponding internal registers.

Active high does not sound like edge sensitive to me. Still, under serial port programming, it reads:

  • (SERIAL I/O PORT PIN DESCRIPTIONS) I/O_UPDATE — Input/Output Update The I/O update initiates the transfer of written data from the serial or parallel I/O port buffer to active registers.

I/O_UPDATE is active on the rising edge, and its pulse width must be greater than one SYNC_CLK period.
     So my questions are:

  1. Is IO_UPDATE edge sensitive for operations other than serial port programming?
  2. Is it possible to set IO_UPDATE permanently high in order to get an output synchronous to SYNC_CLK?
  3. If b) is not possible, can I modulate IO_UPDATE with the same frequency as SYNC_CLK to have an output synchronous to SYNC_CLK or does IO_UPDATE have to be high for more than one SYNC_CLK period, same as for serial port programming?


     2. Parallel port streaming and IO_UPDATE.

     Datasheet: “To accommodate this functionality, the AD9914 provides a register control bit, parallel port streaming enable (0x00[17]).      When this bit is set to Logic 1, the parallel port operates without the need for an I/O update.”

     My question here is:

  1. What does: "Without the need" mean? Is it still possible, during parallel port streaming, to use IO_UPDATE (I need to clear the phase accumulator somehow, and the autoclear phase accumulator functionality will just work with IO_UPDATE).


I would greatly appreciate any help from any side!

Best regards,