Hardware manual

Microcomputer Technical Q&A
109
Q&A No.: QAH8S-232
Category: SCI
Subject: Operation of RDRF Flag
Question
An operation to clear the RDRF flag to 0 in the serial status register (SSR) is necessary in SCI
reception. What will happen if this flag is cleared to 0 directly without first reading 1?
Answer
It will not be cleared. However, if the BCLR instruction is used, after a byte-unit read of SSR, the
RDRF flag is cleared to 0, and a byte-unit write is performed. Therefore, the RDRF flag can be
cleared to 0 with a BCLR instruction when the flag is set to 1 (in the RXI interrupt handling
routine).
Applicable Products
Applicability Series Applicability Series Applicability Series
Entire H8S Series Yes H8S/2655 Yes H8S/2350
Yes H8S/2355 Yes H8S/2357 Yes H8S/2345
Yes H8S/2245 H8S/2148 H8S/2144
H8S/2138 H8S/2134 H8S/2128
H8S/2124 — — — —