This mode of the physical device driver can be controlled independently for each modem control signal. When this mode is enabled, the physical device driver does not give data to the transmit hardware if the modem control signals are OFF (disabled). Data is not transmitted unless all the lines enabled for output handshaking are up.

If one of these modes is enabled, Error Alerts might be generated when the OS/2 Logging Facility is enabled. If an external device causes CTS, DCD, or DSR to become inactive, transmission is blocked while the device driver waits for the respective line to become active again. If the line does not become active before the Write Timeout period expires, an Error Alert is generated.