We have used LTC2846 and LTC2845 for multiprotocol interface. Now we want to add a asynchronous RS232 interface to the original design and the signal only has TX, RX, RTS, CTS, DCD and DTE / DCE functions. May I can only use LTC2844 to design this? Thanks!
The LTC2844 supports three RS-232 transmit and three receive, so it should support your configuration as either DCE or DTE (assuming the DTE/DCE function you mention is the pin on LTC2844 rather than an extra signal to transmit via RS-232).
LTC2844 typically relies on LTC2846 for the VEE (-7V) and VDD (8V) supplies, which appears to be the configuration in your diagram (and 5V supply for VCC) so this should support your application.