User manual

DocID026171 Rev 6 21/79
VL6180X Functional description
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2.8 Range checks
Error codes 6, 8 and 11 in Table 8 are configurable by the user. They can be
enabled/disabled via register SYSRANGE__RANGE_CHECK_ENABLES{0x2D} by setting or
clearing the appropriate bit. The register default is 0x11 i,e, ECE and SNR enabled.
2.8.1 Early convergence estimate (ECE)
Early convergence estimate (ECE) is a programmable feature designed to minimize power
consumption when there is no target in the field-of-view (FOV).
The system is said to have ‘converged’ (i.e. range acquired), when the convergence
threshold
(d)
is reached before the max. convergence time limit (see Figure 13). This ratio
specifies the minimum return signal rate required for convergence. If there is no target in the
FOV, the system will continue to operate until the max. convergence time limit is reached
before switching off thereby consuming power. With ECE enabled, the system estimates the
Table 8. Range error codes
Bits [7:4] Error code Description
Range
(mm)
0 No error Valid measurement 0 - 200
(1)
1. Range overflow occurs typically around 200 mm.
1-5 System error
System error detected. No
measurement possible.
255
6 Early convergence estimate ECE check failed 255
7 Max convergence
System did not converge before the
specified max. convergence time limit
255
8 Range ignore Ignore threshold check failed 255
9-10 Not used - -
11 SNR
Ambient conditions too high.
Measurement invalidated
255
12 Raw range underflow
RESULT__RANGE_RAW < 0
(because offset is programmable a
negative range result is possible)
0
13 Raw range overflow
RESULT__RANGE_RAW is out of range.
This occurs typically around 200 mm
255
14 Range underflow
RESULT__RANGE_VAL < 0
(because offset is programmable a
negative range result is possible)
0
15 Range overflow
RESULT__RANGE_VAL is out of range.
This occurs typically around 200 mm
255
d. For standard ranging, the convergence threshold is set to 15360. The convergence threshold register is not
accessible by the user.