Siemens SIMATIC S7-400 Hardware And Installation Manual page 199

Removing the Connector and Socket Covers
On the right-hand side of a central rack, there is a 120-pin socket for connecting
expansion racks to the ISA bus (see Figure 8-5). This socket is protected by a
screw-mounted metal cover.
The EXM 478, ATM 478, and MSM 478 expansion modules contain
The matching plug on the left side,
An expansion socket on the right side so that other expansion modules can be
plugged in.
Remove the transport protection from the expansion plugs and unscrew the metal
covers from the module expansion sockets which are to accept other expansion
modules.
Figure 8-5 Locations of the Expansion Socket and Plug
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
www.gkbpx.com
e. g. CPU 488-3
Expansion plug
Expansion
socket
Assembling the M7-400
e. g. EXM 478
8-17