Memory system and memory control method

A memory system, comprising:

• a nonvolatile memory including a plurality of memory cells;
• and
• a memory controller configured to control the nonvolatile memory, wherein
• the plurality of memory cells is divided into a plurality of groups, and each group is assigned a threshold read count value from a predetermined range of read count values,
• the memory controller includes:
• an initial value setting circuit configured to set an initial down counter value for each group to a number within a predetermined initial value range,
• a counter configured to track a read count by decrementing the read count for each group at every read operation of the group,
• a determination circuit configured to compare the read count for each group tracked by the counter to the assigned threshold read count value for the group and to determine whether the read count reaches a down counter target value for each group, and
• a nonvolatile memory read/write control circuit configured to read data from the group when the determination circuit indicates that the read count for the group has reached the assigned threshold read count value, and
• zero is set as the down counter target value for all the groups.

A memory system, comprising:

• a nonvolatile memory including a plurality of memory cells;
• and
• a memory controller configured to control the nonvolatile memory, wherein
• the plurality of memory cells is divided into a plurality of groups, and each group is assigned a threshold read count value from a predetermined range of read count values, and
• the memory controller includes:
• a counter configured to track a read count for each group,
• a determination circuit configured to compare the read count for each group tracked by the counter to the assigned threshold read count value for the group,
• a threshold setting circuit configured to assign the threshold read count value for each group by randomly selecting numbers within the predetermined range, a uppermost value of the predetermined range being a value for determining whether to perform a refreshing process, a lowermost value of the predetermined range being smaller than the uppermost value by ten percent, and
• a nonvolatile memory read/write control circuit configured to read data from the group when the determination circuit indicates that the read count for the group has reached the assigned threshold read count value.