Siemens SIMATIC S7-400 Reference Manual page 19

Slot for Interface Modules
You can insert one interface module (IF module) for each CPUs 41x-3 and 41x-4 in
this slot.
Interface for Memory Expansion
CPU 417-4 also features interfaces for memory expansion. These make it possible
to expand the working memory. (See "S7-400, M7-400 Programmable Controllers,
Hardware and Installation" )
MPI/DP interface
You can connect the following devices to the MPI of the CPU, for example:
• Programming devices
• Operation and monitoring devices
• Additional S7-400 or S7-300 controllers (see Section 1.6).
Use the bus connector with an angular outgoing cable (see the Installation manual,
Chapter 7)
You can also configure the MPI interface as a DP master and use it as a
PROFIBUS DP interface with up to 32 DP slaves.
PROFIBUS DP interface
You can connect the distributed I/O, programming devices/OPs and additional
DP master stations to the PROFIBUS DP interface.
Automation System S7-400 CPU Specifications
A5E00165965-01
Structure of a CPU 41x
1-7