Maxim Integrated MAXQ7667 - Manual (Page 162)

8.5.7 UART Receive Data Example
To receive serial data using the UART, the SBUF register is read. To ensure the data has been written, the application code should
examine the receive interrupt (RI) flag immediately before reading the SBUF register. The application code can wait until the data has
been completely shifted in to the receive buffer and the RI flag is set indicating new data has been received. The following example
details the method to prevent reading before the register is full.
• Wait until the RI bit (SCON.0) is set.
• Clear the RI bit by setting it to 0.
• Read data from SBUF register.
8.5.8 Setting UART Baud Rate
The UART baud rate is set with the BT register. The baud rate is derived from the system clock that can be the external crystal for baud-
rate accuracy. To set baud rate, the following equation is used.
Baud rate = (BT x FREQ)/(2 23 /2 (SMOD x 2) )
where BT is the Bus Timing register and FREQ is the system clock frequency.
For example, to set the baud rate for 115,200 with the system clock set to the external 16MHz crystal. The mode is asynchronous,
therefore, SMOD = 1. Using the above equation and solving for BT we get the following:
Baud = (BT x 16,000,000)/(2 23 /2 2 ) ≥ BT x (16,000,000/2,097,152) = 115,200 then
BT = 115,200 x 2,097,152/16,000,000 ≥ 15,099.4944
Round down to 15,099 as the BT register only holds integers.
Then, 15,099 = 0x3AFB hex
Load the BT register with = 0x3AFB
To verify, plug the 15,099 value back into the equation to compute the exact baud rate. The exact baud rate using the BT divider is
115,196.228 baud (well within 0.01% tolerance) and should work perfectly.
8.5.9 UART FIFO
The UART FIFO operates exactly the same as the LIN FIFO. The setup and use is detailed in Section 8.4.8: LIN Transmit and Receive
FIFO.
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MAXQ7667 User’s Guide