PRINT option and print control bit

Writing to a 3270 display or printer updates the device buffer. On a display, the results are reflected immediately on the screen, which is a driven from the buffer. For a printer, however, there might be no visible effect, because printing does not occur until you turn on the appropriate bit in the “write control character”.

The WCC is part of the 3270 data stream; see The output datastream . For BMS, you turn on the print bit by specifying the PRINT option on a SEND MAP, SEND TEXT, or SEND CONTROL command, or in the map used with SEND MAP. If you are using terminal control SENDs, you must turn on the print bit with the CTLCHAR option.

A terminal write occurs on every terminal control SEND, and on every SEND MAP, SEND TEXT, or SEND CONTROL unless you are using the ACCUM or PAGING options. ACCUM delays writing until a page is full or the logical message is ended. When you use ACCUM, you should use the same print options on every SEND command for the same page. PAGING defers the terminal writes to another task, but they are generated in the same way as without PAGING.

The fact that printing does not occur until the print bit is on allows you to build the print buffer in stages with multiple writes and to change data or attribute bytes already in the buffer. That is, you can use the hardware to achieve some of the effects that you get with the ACCUM option of BMS. The NLEOM option affects this ability, however; see the discussion at NLEOM option.