Renesas H8S/2138 Series Handbuch Seite 129

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Microcomputer Technical Q&A
121
Q&A No.: QAH8S-240
Category: SCI
Subject: Data Transfer to TDR
Questions
SRAM
H8S Series chip
Data
transmission SCI
DMAC or DTC
16-bit data bus
Transfer data
To transfer data in 16-bit-access space* to the SCI transmit data register (TDR: 8 bits long), as
shown above:
1. Is there any way of performing the transfer by software?
2. Is there any way of performing the transfer with the DMAC?
Note: * The H8S/2138, H8S/2134, H8S/2128, and H8S/2124 Series have only 8-bit-access space.
Answers
1. Transfer by software
Byte access can also be used in 16-bit-access space. Read the transfer data in SRAM one byte
at a time, and transfer it to the SCI’s TDR (using the MOV.B instruction).
2. Transfer using DMAC or DTC
Designate the TXI interrupt as the DMAC or DTC activation source, set the data size as byte,
and transfer the transfer data in SRAM to the SCI’s TDR one byte at a time. (Word-size
transfer is not possible, since the DMAC or DTC is activated each time one byte is
transmitted.)
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