The S7A driver is a GE version 7.x I/O driver developed by Industrial Communications Solution. It provides the interface and communications protocol between Siemens S7 - 300/400 PLC systems and your process control software.
The S7A driver supports datablock numbers up to 4095. If you add more than 4095 datablocks to the target database for the S7A driver, the database will fail the I/O addresses that exceed this number.
For detailed information, refer to the S7A online help.