LM3S328 Datasheet, PDF (237/371 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S328 Data Sheet
bits (LSB first), parity bit, and the stop bits according to the programmed configuration in the
control registers. See Figure 12-2 for details.
The receive logic performs serial-to-parallel conversion on the received bit stream after a valid
start pulse has been detected. Overrun, parity, frame error checking, and line-break detection are
also performed, and their status accompanies the data that is written to the receive FIFO.
Figure 12-2. UART Character Frame
UnTX
1-2
LSB
1
MSB
0
5-8 data bits
stop bits
n
Parity bit
Start
if enabled
12.2.2
Baud-Rate Generation
The baud-rate divisor is a 22-bit number consisting of a 16-bit integer and a 6-bit fractional part.
The number formed by these two values is used by the baud-rate generator to determine the bit
period. Having a fractional baud-rate divider allows the UART to generate all the standard baud
rates.
The 16-bit integer is loaded through the UART Integer Baud-Rate Divisor (UARTIBRD) register
(see page 248) and the 6-bit fractional part is loaded with the UART Fractional Baud-Rate
Divisor (UARTFBRD) register (see page 249). The baud-rate divisor (BRD) has the following
relationship to the system clock (where BRDI is the integer part of the BRD and BRDF is the
fractional part, separated by a decimal place.):
BRD = BRDI + BRDF = SysClk / (16 * Baud Rate)
The 6-bit fractional number (that is to be loaded into the DIVFRAC bit field in the UARTFBRD
register) can be calculated by taking the fractional part of the baud-rate divisor, multiplying it by 64,
and adding 0.5 to account for rounding errors:
UARTFBRD[DIVFRAC] = integer(BRDF * 64 + 0.5)
The UART generates an internal baud-rate reference clock at 16x the baud-rate (referred to as
Baud16). This reference clock is divided by 16 to generate the transmit clock, and is used for
error detection during receive operations.
Along with the UART Line Control, High Byte (UARTLCRH) register (see page 250), the
UARTIBRD and UARTFBRD registers form an internal 30-bit register. This internal register is only
updated when a write operation to UARTLCRH is performed, so any changes to the baud-rate
divisor must be followed by a write to the UARTLCRH register for the changes to take effect.
To update the baud-rate registers, there are four possible sequences:
„ UARTIBRD write, UARTFBRD write, and UARTLCRH write
„ UARTFBRD write, UARTIBRD write, and UARTLCRH write
„ UARTIBRD write and UARTLCRH write
„ UARTFBRD write and UARTLCRH write
April 27, 2007
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Preliminary