Siemens 500 NIM - Manual (Page 120)

PM550 CIM Requirements A-3 SIMATIC TIWAY I Series 500 NIM User Manual
A.2 Local Line Length
The PM550 CIM supports operation over the Local Line at distances up to
10,000 feet and 9600 baud.
Advances in technology have provided line drivers and receivers that
support Local Line operation up to 25,000 feet. These new drivers have been
incorporated in TIWAY I Conformant devices to support the extended
operation. However, in networks containing the PM550 CIM, which is not a
TIWAY I conformant device, the Local Line length is restricted to 10,000
feet and 9600 baud.