Table of Contents
Advertisement
CHAPTER 17 UART
17.7.1
Operation in Asynchronous Mode (Operation Modes 0
and 1)
When UART is used in operation mode 0 (normal mode) or operation mode 1
(multiprocessor mode), the asynchronous transfer mode is selected.
■ Operation in Asynchronous Mode
●
Transfer data format
Transfer data begins with the start bit (L level) and ends with the stop bit (H level). The data of the
specified data bit length is transferred in LSB first mode.
• In operation mode 0, the length of data with no parity is fixed to 7 bits, and that of data with parity is
fixed to 8 bits.
• In operation mode 1, the length of data is fixed to 8 bits with an address/data (A/D) selection bit added
instead of parity.
Figure 17.7-1 shows the data format in asynchronous mode.
Figure 17.7-1 Transfer Data Format (Operation Modes 0 and 1)
[Operation mode 0]
[Operation mode 1]
* : D7 (bit 7) when parity is not provided
P (parity) when parity is provided
ST : Start bit
SP : Stop bit
A/D : Address/data selection bit in operation mode 1 (multiprocessor mode)
●
Transmission operation
Transmission data is written to the output data register (SODR0/SODR1) when the transmission data empty
flag bit (SSR0/SSR1: TDRE) is "1". This data is transmitted if the transmission operation is enabled
(SCR0/SCR1: TXE = 1).
The TDRE flag is again set to "1" when the transmission data is transferred to the transmission shift register
and its transmission starts. Then, the next piece of transmission data gets ready to be set. At this point, a
transmission interrupt request is output requesting that the next piece of transmission data be set in the
SODR0/SODR1 register if that request is enabled (SSR0/SSR1: TIE = 1). The TDRE flag is cleared to "0"
when the transmission data is written to SODR0/SODR1.
500
ST
D0
D1
D2
D3
ST
D0
D1
D2
D3
*
D4
D5
D6
D7/P SP
D4
D5
D6
D7
A/D
SP
Advertisement
Table of Contents
