modbus question

i read this 2 statement as a note in a DELTA RTU catalogue. i cant understand the meaning!! could anyone describe it more???

NOTE:
1. RTU-485 can only read and write one AI/AO extension unit at the same time.
2. RTU-485 is able to read/write maximum 16 words at a time in the communication control.

Means that if you have more analog modules, e.g. 2 x 8 AI then you would have to r/w in 2 cycles. Same goes if you want to r/w mire than 16 words. So if you have 2 ext. with 32 words each then you would need 4 cycles to read all. (hint: use a counter for addressing)

Thank you balash