As mentioned in the ET200M Manual That

The IM 153-2 provides changed input signals with the respective current time and saves this in a buffer (message list). Such a message list is a data record with maximum 20 messages about time-stamped signal changes. Up to 15 data records can be saved in the IM 153-2.

I have a ´query that as 20 messages upto 15 data records can be saved in IM153-2, is it mean that 15x20= 300 signals can be time stamped in one cycle.

Can any one please clrear the concept of message buffer in IM153-2. How it works and what exactly this 300 mean?