No Handshaking/Full Duplex Modem

Howdy all,
Can anyone tell me the difference between the "No Handshaking" and "Full Duplex Modem" setting for an AB Micrologix 1200.
The Comm settings are DF1 Full Duplex 19200,N,8,1.

My hypothesis is that "Full Duplex Modem" crosses Rx & Tx and "No Handshking" does not. This is only a guess though. Any help would be great. Thanks...

Full Duplex:
Refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time.

A null modem uses crossed wires, its a way to connect to computers or devices directly without the use of a modem but in the same manner as if you were using one.

A modem handshake is what occurs when the receiving modem answers the phone call and the two modems begin to communicate. Before anything else happens, the modems must evaluate the quality of the line, negotiate error control protocols and data compression that they can both recognize, and work out what the most suitable connection speed should be, based on the conditions. This process is called the handshake. If the modem's internal speaker is turned up, you'll hear the handshake as screeches, bells, and whistles. Once that has happened, the modems send data back and forth between the two computers. The modem that initiates the connection sends data in a lower frequency range and listens for the response in a higher range, corresponding to the recieving modem.

No handshake means it doesnt need to go thru that routine when connecting this is an option with Full Duplex that isnt always needed.