Precautions - NEC V850E/IA1 mPD703116 User Manual

32-bit single-chip microcontrollers

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(5) Transfer rate during continuous transmission

During continuous transmission, the transfer rate from a stop bit to the next start bit is extended two clocks of

base clock longer than normal. However, on the reception side, the transfer result is not affected since the

timing is initialized by the detection of the start bit.

Figure 10-14. Transfer Rate During Continuous Transmission

Representing the 1-bit data length by FL, the stop bit length by FLstp, and the base clock frequency by f

yields the following equation.

FLstp = FL + 2/f

Therefore, the transfer rate during continuous transmission is as follows.

Transfer rate = 11 × FL = 2/f

10.2.7 Precautions

Precautions to be observed when using UART0 are shown below.

(1) When the supply of clocks to UART0 is stopped (for example, IDLE or STOP mode), operation stops with each

also holds and outputs the value it had immediately before the supply of clocks was stopped. However,

operation is not guaranteed after the supply of clocks is restarted. Therefore, after the supply of clocks is

restarted, the circuits should be initialized by setting UARTCAE0 bit = 0, RXE0 bit = 0, and TXE0 bit = 0 in the

ASIM0 register.

(2) UART0 has a 2-stage buffer configuration consisting of transmission buffer register 0 (TXB0) and the

transmission shift register, and has status flags (TXBF0 and TXSF0 bits of ASIF0 register) that indicate the

status of each buffer. If the TXBF0 and TXSF0 bits are read in continuous transmission simultaneously, their

values change from "10" to "01", but since this change timing is in the period in which data is shifted from TXB0

to the transmission shift register, "11" or "00" may be read, depending on the timing. Thus, read only the

TXBF0 bit during continuous transmission.

CHAPTER 10 SERIAL INTERFACE FUNCTION

1 data frame

User's Manual U14492EJ3V0UD

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