TI中文支持网在TI28335的SCI技术手册里写到：
在这里写那个don't care data是什么用途？是作为block-start signal传送出去吗？如果是的话为什么在2中又说到
The first data word written is suppressed while the block-start signal is
sent out and ignored after that. 如果不是的话那到底block-start signal是什么？
Johnson Chen1：
Block start signal 有下面两种方法:
Method 1: Deliberately leave an idle time of ten bits or more by delaying the time between thetransmission of the last frame of data in the previous block and the transmission of the address frameof the new block.
2. Method 2: The SCI port first sets the TXWAKE bit (SCICTL1, bit 3) to 1 before writing to theSCITXBUF register. This sends an idle time of exactly 11 bits. In this method, the serialcommunications line is not idle any longer than necessary. (A don’t care byte has to be written toSCITXBUF after setting TXWAKE, and before sending the address, so as to transmit the idle time.)
说白了就是就是在上一block 和发送帧之前保持10个一号的空闲时间。
don't care data 的意思就是这个数据是无效的（可以写任意数据），不会被从发到数据线上去，因为已经置了TXWAKE位。
这样做的method 2..
