How a HP-IL peripheral signals "no more data"

[cgh]

I am writting a IL peripheral for ILPER (just to learn how it works), and I am facing witn the following problem:

When the peripheral is requested to return data (ENTER [71/75] or INA [41]), if it sends an EOT, this works on 41, but not on the 71/75 who sends indefintelly a SDA command (the device returns EOT ).
I read in "The HP-IL System" book that a end-Byte exists (0x01xxxxxxxxx). If I use it, its works on 71/75 (but ENTER n;A$ will clear A$), and not on 41; this raises a TRANSMIT ERR.
So my question is: what the good way for peripheral to answer that there is no data available on reading ?
I assume that the functions SPOLL() could be used for checking this (I have implemented a status bit set if data are still available), but, on a simple 75C or 41C, the function does not exists... (INSTAT can do the job and it is present inside the HP82160A module).
What is the best usage to read data with HP-IL peripherals ?

Sorry for my question of "newbie"

Thanks a lot for your help.

Christophe