9.3.5.2 Manual Input Selection
There are two manual input selection modes that can be set by a register: Manual with Auto-Fallback and Manual with Auto-Holdover. In either manual mode, the input selection can be done through register control (Table 6) or hardware pin control (Table 7).
- Manual with Auto-Fallback: In this mode, the manually selected reference is the active reference until it becomes invalid. If the reference becomes invalid, the DPLL will automatically fallback to the highest priority input that is valid or qualified. If no prioritized inputs are valid, the DPLL will enter holdover mode (if tuning word history is valid) or free-run mode. The DPLL will exit holdover mode when the selected input becomes valid.
- Manual with Auto-Holdover: In this mode, the manually selected reference is the active reference until it becomes invalid. If the reference becomes invalid, the DPLL will automatically enter holdover mode (if tuning word history is valid) or free-run mode. The DPLL will exit holdover mode when the selected input becomes valid.
Table 6. Manual Input Selection by Register Bits
DPLLx_REF_MAN_REG_SEL[2:0] BITS |
DPLLx_REF_MAN_SEL BIT |
SELECTED INPUT |
000b |
0 |
IN0 |
001b |
0 |
IN1 |
010b |
0 |
IN2 |
011b |
0 |
IN3 |
100b |
0 |
VCO1 Loopback to DPLL2 |
101b |
0 |
VCO2 Loopback to DPLL1 |
Table 7. Manual Input Selection by Hardware Pins
INSELx_[1:0] PINS |
DPLLx_REF_MAN_SEL BIT |
SELECTED INPUT |
00b |
1 |
IN0 |
01b |
1 |
IN1 |
10b |
1 |
IN2 |
11b |
1 |
IN3 |
The reference input selection flowchart is shown in Figure 35.