Siemens SIMATIC Ident Function Manual page 120

Appendix
A.2 Connection of serial devices via Freeport protocol
Notes on the commands and functions
Reset_Univ
Communication with the CM is initialized with the Reset command. The Reset command
does not have reader-specific parameters and triggers the deletion of the buffers.
After the "Reset_Univ" the communication module is ready for operation.
Read
When the "Read" command is started, the data that the CM has already received is
transferred to the controller.
If the "Read" command is started before the CM has received data, the command
remains active until the CM has received data that is then transferred to the controller.
An active "Read" command can be canceled with a "Reset_*"/"Write_Config" command.
The presence bit ("TP") indicates that the CM has received new data and that this data
is available for fetching with a "Read" command. After data transmission to the
controller, the presence bit is reset unless new data has already been received.
When doing this, note the buffer size and the buffer overflow. If the receive buffer of the
CM is full, existing data is overwritten by newly received data.
120
Ident profile, Add-on instruction for Rockwell systems
Function Manual, 07/2020, C79000-G8976-C410-04