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Clock asynchronous serial I/O (UART) mode
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(2) Clock asynchronous serial I/O (UART) mode
The UART allows transmitting and receiving data after setting the desired transfer rate and transfer data
format. Table 26 lists the specifications of the UART mode. Figure 84 shows the UARTi transmit/receive
mode register.
Table 26. Specifications of clock synchronous serial I/O mode
Item
Specification
Transfer data format
Character bit (transfer data): 7 bits, 8 bits or 9 bits as selected
Start bit: 1 bit
Parity bit: Odd, even or nothing as selected
Stop bit: 1 bit or 2 bits as selected
When internal clock is selected (bit 3 at addresses 03A0
16
, 03A8
16
= “0”) :
fi/16(n+1) (Note 1)
fi = f
1
, f
8
, f
32
When external clock is selected (bit 3 at addresses 03A0
16
, 03A8
16
=“1”) :
f
EXT
/16(n+1) (Note 1) (Note 2)
CTS function/RTS function/CTS, RTS function chosen to be invalid
To start transmission, the following requirements must be met:
- Transmit enable bit (bit 0 at addresses 03A5
16
, 03AD
16
) = “1”
- Transmit buffer empty flag (bit 1 at addresses 03A5
16
, 03AD
16
) = “0”
- When CTS function is selected, CTS input level = “L”
To start reception, the following requirements must be met:
- Receive enable bit (bit 2 at addresses 03A5
16
, 03AD
16
) = “1”
- Start bit detection
When transmitting
- Transmit interrupt cause select bits (bits 0,1 at address 03B0
16
) = “0”:
Interrupts requested when data transfer from UARTi transfer buffer register to
UARTi transmit register is completed
- Transmit interrupt cause select bits (bits 0, 1 at address 03B0
16
) = “1”:
Interrupts requested when data transmission from UARTi transfer register is completed
When receiving
- Interrupts requested when data transfer from UARTi receive register to
UARTi receive buffer register is completed
Overrun error (Note 3)
This error occurs when the next data is ready before contents of UARTi receive
buffer register are read out
Framing error
This error occurs when the number of stop bits set is not detected
Parity error
This error occurs when if parity is enabled, the number of 1’s in parity and
character bits does not match the number of 1’s set
Error sum flag
This flag is set (= 1) when any of the overrun, framing, and parity errors is encountered
Sleep mode selection
This mode is used to transfer data to and from one of multiple slave microcomputers
Note 1: ‘n’ denotes the value 00
16
to FF
16
that is set to the UARTi bit rate generator.
Note 2: f
EXT
is input from the CLKi pin.
Note 3: If an overrun error occurs, the UARTi receive buffer will have the next data written in. Note also
that the UARTi receive interrupt request bit is not set to “1”.
Transfer clock
Transmission/reception control
Transmission start condition
Reception start condition
Interrupt request
generation timing
Error detection
select function