Wiznet W7500 Reference Manual page 294

This register contains the value from which the counter is to decrement. This
is the value used to reload the counter when Periodic mode is enabled, and
the current count reaches 0.
This register provides an alternative method of accessing the TimerLoad
Register. The difference is that writes to TimerBGLoad Register do not cause
the counter to immediately restart from the new value.
Reading from this register returns the same value returned from TimerLoad
Register.
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W7500x Reference Manual Version1.1.0