SBAS940 December 2018 DAC8742H
The behavior of the UART interface changes based on whether the device is operating in HART mode or in FOUNDATION FIELDBUS and PROFIBUS PA mode.
In HART mode, the device expects 1 start bit, 8 data bits, 1 odd parity bit, and 1 stop bit or an 8O1 UART character format. The transmit path of the device acts as a direct feedthrough of the UART input to the HART FSK output, therefore the UART BAUD rate from the host controller must be 1200Hz ±1% as required by the HART standard. The receive path of the device will also operate at 1200Hz ±1%.
In FOUNDATION FIELDBUS and PROFIBUS PA mode the UART interface expects 1 start bit, 8 data bits, no parity bit, and 1 stop bit or an 8N1 UART character format. In this mode the UART interfaces transmit and receive FIFOs so the BAUD rate is not required to match the 31.25 kHz BAUD used by FOUNDATION FIELDBUS and PROFIBUS PA. In this mode the expected transmit and receive UART BAUD is 57.6 Hz ±2.5%.