Asynchronous (Start-Stop Synchronous) Mode - Fujitsu F2MC-16LX Hardware Manual

17.4.2 Asynchronous (Start-stop Synchronous) Mode

In the asynchronous (start-stop synchronous) mode, transfer data always begins with
a start bit ("L" level data) and ends with a stop bit ("H" level data).
■ Transfer Data Format
The UART handles only data of a NRZ (non return to zero) format. Figure 17.4-1 shows the
transfer data format.
SIN, SOT
Transfer data always begins with a start bit ("L" level data), is transmitted in the data bit length
specified by the LSB first and ends with a stop bit ("H" level data). If the external clock is
selected, always enter a clock.
In the normal mode (mode 0), the data length can be set to 7 or 8 bits. In the multiprocessor
mode (mode 1), however, the data length must be set to 8 bits. Also, no parity bit can be added
in the multiprocessor mode. Instead, an A/D bit is always added to data.
■ Receiver Operation
If the RXE bit of the SCR register is "1", a receiver operation is always performed. Once a start
bit is detected, one-frame data is received according to the data format specified by that
register. If an error occurs at the end of one-frame data reception, an error flag is set and the
RDRF flag of the SSR register is then set. If the RIE bit of the SSR register is set to "1"
simultaneously, a receiver interrupt occurs to the CPU. The flags of the SSR register are
checked. If the receiver is normal, data is read from the SIDR register; if an error occurs, take
corrective actions accordingly.
register.
❍ Start bit detection method
Specify settings as follows for start bit detection:
• Immediately before the start of the communication period, be sure to set the communication
line to "H" (mark level added).
• Set receive ready (RXE=H) while the communication line is at "H" (mark level).
• Do not set receive ready (RXE=H) during the non-communication period (mark level
removed). Otherwise, data is not received correctly.
• When the stop bit is detected (the RDRF flag is set to "1"), set receive not ready (RXE=L)
while the communication line is at "H" (mark level).
Figure 17.4-1 Transfer Data Format (Modes 0 and 1)
0 1 0 1 1
LSB
Start
Transferred data is 01001101
The RDRF flag is cleared by reading data from the SIDR
0 0 1 0 1 1
MSB Stop
A/D Stop
.
B
17.4 UART Operations
(Mode 0)
(Mode 1)
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