X3T9.2/87-202 rev 2 wording is as follows:


The maximum burst size field indicates the maximum amount of data that the 
target shall transfer during a data in or data out phase before disconnecting. 
This value is expressed in increments of 512 bytes (e.g. a value of one 
implies 512 bytes and a value of two implies 1024 bytes).  The target may 
round this value as specified in section 6._._.  A value of zero indicates no 
limit on the amount of data transferred.

If disconnect is not enabled by the initiator, the target may treat this field 
as if the value is set to zero.

If the target does not support disconnect during data transfers, the target 
shall report this value as non-changeable and zero.