
EM358x
Rev. 0.4
99
SC_UARTODD specifies whether transmitted and received parity bits contain odd or even parity. If this bit is
clear, the parity bit is even, and if set, the parity bit is odd. Even parity is the exclusive-or of all of the data bits,
and odd parity is the inverse of the even parity value. SC_UARTODD has no effect if SC_UARTPAR is clear.
A UART character frame contains, in sequence:
The start bit
The least significant data bit
The remaining data bits
If parity is enabled, the parity bit
The stop bit, or bits, if 2 stop bits are selected.
Figure 8-3 shows the UART character frame format, with optional bits indicated. Depending on the options
chosen for the character frame, the length of a character frame ranges from 9 to 12 bit times.
Note that asynchronous serial data may have arbitrarily long idle periods between characters. When idle, serial
data (TXD or RXD) is held in the high state. Serial data transitions to the low state in the start bit at the beginning
of a character frame.
Figure 8-3. UART Character Frame Format
8.6.3
FIFOs
Characters transmitted and received by the UART are buffered in the transmit and receive FIFOs that are both 4
entries deep (see Figure 8-4). When software writes a character to the SC1_DATA register, it is pushed onto the
transmit FIFO. Similarly, when software reads from the SC1_DATA register, the character returned is pulled from
the receive FIFO. If the transmit and receive DMA channels are used, the DMA channels also write to and read
from the transmit and receive FIFOs.
Figure 8-4. UART FIFOs
8.6.4
RTS/CTS Flow control
RTS/CTS flow control, also called hardware flow control, uses two signals (nRTS and nCTS) in addition to
received and transmitted data (see Figure 8-5). Flow control is used by a data receiver to prevent buffer overflow,
by signaling an external device when it is and is not allowed to transmit.
Содержание EMBER EM358 series
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