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The time-guard feature enables the UART interface to operate with slow remote devices.
When set, it will insert a number of idle states between transmitting two characters, the length of which can be set in the UART_TIMEGUARD register. The value in the register defines the number of baud clocks of idle period to insert.
This idle state essentially acts like a long stop bit. In UART and synchronous modes, a Timeguard is added in addition to the stop bit. In ISO7816 there is a waiting period rather than an actual stop bit. Software should set 1-2 or more Timeguard cycles according to the protocol used and the card requirements.