请问串口的SR寄存器里的状态位为什么只有CTS判断的
时间：10-02
整理：3721RD
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请问串口的SR寄存器里的状态位为什么只有CTS判断的，没有RTS，在CR寄存器里也没有位是对RTS进行操作的，难道是要直接对GPIO置1和0进行操作吗?
手册里控制寄存器有一位是这样的，
RTSE: RTS enable
0: RTS hardware flow control disabled
1: RTS interrupt enabled, data is only requested when there is space in the receive buffer.
The transmission of data is expected to cease after the current character has been
transmitted. The nRTS output is asserted (tied to 0) when a data can be received.
Note: This bit is not available for UART4 & UART5.
这里说到一个receive buffer.请问是硬件的还是软件的