MLC nonvolatile memory writing limitations.

The number of write cycles as with most nonvolatile memory is rated for 100,000 write cycles. Read cycles are unlimited. This is sufficient for many years of use in most applications. To reduce the number of writes a temporary memory register is used for the value and the parameter that is changed. One temporary register is used for each loop control module. The MLC will use the value in the temporary register without writing the value to the nonvolatile memory until the parameter changes or until power down. Value changes do not cause the data to be written to the nonvolatile memory. If the parameter changes or the MLC is powered down it will write the data to the nonvolatile memory.

To illustrate:

Example #1:

SP = 100
SP = 101
SP = 102
SP = 103
SP = 104
SP = 105

No write cycles would be used since the parameter did not change (the values remained in temporary storage).

Example #2

SP = 100
ALM1 = 110
SP = 101
ALM1 = 111
SP = 102
ALM1 = 112
SP = 103
ALM1 = 113
SP = 104
ALM1 = 114
SP = 105
ALM1 = 115
Power Down

(13) Write cycles would be consumed in the above example. A deviation alarm set to 10 would have reduced the number of write cycles to 1 (Caused by the power down). Using the ramp setpoint feature available within the MLC can also be used to reduce the number of write cycles.