The DELAY_TYPE attribute set to VARIABLE selects the variable tap delay line (Table 1). In VARIABLE mode, the CE and INC pins are used to manually increment and decrement the delay line tap per tap (INC/DEC increments/decrements one tap at a time). The tap delay increments by setting CE = 1 and INC = 1, or decrements by CE = 1 and INC = 0. The increment/decrement operation depends on the UPDATE_MODE attribute (see Figure 1). The EN_VTC pin should be held Low during the delay change command to ensure that any automatic adjustments are stopped.
To increment/decrement delay lines when using TIME mode, use the following procedure (see Figure 1):
- Deassert (Low) the EN_VTC pin.
- Wait a minimum of 10 clock cycles.
- Use the CE and INC ports to increment or decrement the delay line.
- Wait a minimum of 5 clock cycles.
- (Option for multiple updates) Increment or decrement of the delay line needs to be performed. Go to step 3, or else proceed to step 6.
- Wait a minimum of 10 clock cycles.
- Assert the EN_VTC pin.
When using the delay line in COUNT mode, the EN_VTC port is always Low. Use the TIME mode procedure in step 2 through step 4 in this section.