
S3C3410X RISC MICROPROCESSOR
UART
9-5
Baud Rate Generation
The UART's baud-rate generator provides the serial clock for transmitter and receiver. The source clock for the
baud-rate generator should be the S3C3410X's internal system clock. The baud-rate clock is generated by
dividing the source clock by 16 and a 16-bit divisor specified by the UART baud-rate divisor register (UBRDIV).
The UBRDIV can be determined as follows:
UBRDIV = (round_off) { MCLK / ( Transfer rate
× 16 ) } – 1
Where the divisor should be from 1 to (2
16 – 1). For example, if the baud-rate is 115200bps and MCLK is 40MHz,
UBRDIV is:
UBRDIV = (int) { MCLK / ( Transfer rate
× 16 ) + 0.5 } – 1
= (int) { 40000000 / ( 115200 * 16 ) + 0.5 } – 1 = (int) ( 21.7 + 0.5 ) – 1
= 22 – 1 = 21
Loop Back Mode
The S3C3410X UART can support a test mode, so called the loop back mode. In this mode, the transmitted data
from UART Tx module is immediately received through UART Rx module via internal connection between Tx
and Rx module. This feature allows that the processor can verify the internal transmit/receive data path of UART
channel. This mode can be selected by setting the loop back bit in the UART control register(UCON).
Infra Red(IrDA) Mode
The UART in S3C3410X can support the frame of infra-red (IrDA) transmit and receive, which can be selected
by setting the infra-red bit in the UART control register (UCON). As shown in Figure 9-4, we should have IrDA Tx
Encoder and Rx Decoder, which is different from the normal UART operation mode. By using the specific
Decoder/Encoder for IrDA, the signal frame in IrDA is different from the normal signal frame of UART, which is
shown in Figure 9-5, 9-6 and 9-7. In IrDA transmit mode, the transmitter should pulse 3/16 duty to represent a
zero data as shown in Figure 9-6. In IrDA receive mode, the receiver should detect the 3/16 pulsed period to
recognize a zero data as shown in Figure 9-7.
IrDA Tx
Encoder
IrDA Tx
Encoder
TxD
IRS
RxD
RE
UART
Block
UTXD
URXD
0
1
0
1
Figure 9-4. IrDA Function Block Diagram