Siemens Simatic S7-400 - Manual (Page 442)

CPUs for M7-400
11-14
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
11.3.6 Expansion Socket
Introduction
The CPU 486-3 and CPU 488-3 are each equipped with an expansion socket. The
ISA bus is continued via the expansion socket.
Which Expansions Can Be Connected?
One EXM 478 extension module with up to three interface submodules, one
MSM 478 mass storage module with diskette and hard disk drives, or one ATM 478
AT adapter module for short AT cards can be connected direct to the CPUs.
A total of up to three expansions can be connected in series to the CPU.
If three EXM 478 expansion modules are connected, up to 11 interface
submodules can be operated together with the slots on each CPU (see
Section 11.3.4).