RS232 電位
-3V ~ -25V = 負電位 = 邏輯 1 = Marking = 斷開
+3V ~ +25V = 正電位 = 邏輯 0 = Spacing = 導通
TTL 電位
0V = 邏輯 0 = Spacing = 導通
5V = 邏輯 1 = Marking = 斷開
Linux
status |= TIOCM_RTS: +12V(RS232) = 正電位 = 邏輯 0 = 0V(TTL)
status &= ~TIOCM_RTS: -12V(RS232) = 負電位 = 邏輯 1 = 5V(TTL)
RTS訊號為負動作
