Siemens SIMATIC S7 System Manual page 466

Communication
8.6 RS485
Freeport mode is active only when the CPU is in RUN mode. Setting the CPU to STOP
mode halts all Freeport communication, and the communication port then reverts to the PPI
protocol with the settings which were configured in the system block of the CPU.
Note
Since the compact CRs models (CR20s, CR30s, CR40s and CR60s) have no Ethernet port,
the RS485 port is the programming port. This creates a conflict if the user program is using
the RS485 port for Freeport. While the user program is using the RS485 port for Freeport,
STEP 7-Micro/WIN SMART V2.3 cannot communicate to the the CPU.
Attaching a USB-PPI cable to the CPU's RS485 port forces the CPU to exit Freeport mode
and enable PPI mode. This allows STEP 7-Micro/WIN SMART V2.3 to regain control of the
the CPU.
If you have attached a USB-PPI cable to the CPU's RS485 port, the CPU cannot enable
Freeport. The CPU will not automatically restart Freeport when you remove the USB-PPI
cable.
The CPU utilizes pin 9 of the RS485 connector to detect when you connect a USB-PPI
cable. Only the CRs models perform the check for USB-PPI cables. The ST and SR models
ignore the state of pin 9. Ensure that any cables used for Freeport do not connect to pin 9 for
the CRs models.
466
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART