Use the contention-resolution feature of TN3270E

TN3270E (Enhanced) is an enhanced form of the TN3270 protocol that allows users to specify an LU or LU pool to which the session will connect and that also supports the Network Virtual Terminal (NVT) protocol for connecting to servers in ASCII mode (for example, in order to log on to a firewall).

Contention-resolution mode is an optional feature of TN3270E, supported by some but not all TN3270E servers, that solves the client's problem of not knowing when the host has finished updating the application screen. If the client is running a TN3270E session and is connected to a server that supports contention-resolution, then the macro runtime does not recognize a new macro screen until the host has finished updating the application screen.

In Z and I Emulator for Web you can set a 3270 Display session to use TN3270E rather than TN3270 by clicking the appropriate radio button on the Connection configuration window of the 3270 Display session configuration panel.

Normally Z and I Emulator for Web automatically communicates in contention-resolution mode with a TN3270E server, if the server supports it. However, you can disable contention-resolution mode with an HTML parameter (see NegotiateCResolution in the online help).