In sensing a group of cells in a multi-state nonvolatile memory, multiple
sensing cycles relative to different demarcation threshold levels are
needed to resolve all possible multiple memory states. Each sensing cycle
has a sensing pass. It may also include a pre-sensing pass or sub-cycle
to identify the cells whose threshold voltages are below the demarcation
threshold level currently being sensed relative to. These are higher
current cells which can be turned off to achieve power-saving and reduced
source bias errors. The cells are turned off by having their associated
bit lines locked out to ground. A repeat sensing pass will then produced
more accurate results. Circuitry and methods are provided to selectively
enable or disable bit-line lockouts and pre-sensing in order to improving
performance while ensuring the sensing operation does not consume more
than a maximum current level.