Asus Z9NA-D6 - Manual (Page 51)

ASUS Z9NA-D6 2-31
8. Serial port connectors (10-1 pin COM2)
These connectors are for the serial (COM) ports. Connect the serial port
module cable to one of these connectors, then install the module to a slot
opening at the back of the system chassis.
9. TPM connector (20-1 pin TPM1)
This connector supports a Trusted Platform Module (TPM) system, which can
securely store keys, digital certificates, passwords, and data. A TPM system
also helps enhance network security, protects digital identities, and ensures
platform integrity.