Communication with a 3270 device occurs through its character buffer, which is a hardware storage mechanism similar to the memory in a processor. Output to the 3270 is sent to the buffer. The buffer, in turn, drives the display of a display terminal and the print mechanism of a printer terminal.
Conversely, keyboard input reaches the host through the buffer, as explained in Input from a 3270 terminal.
Each position on the screen corresponds to one in the buffer, and the contents of that buffer position determine what is displayed on the screen. When the screen is formatted in fields, the first position of each field is used to store certain display characteristics of the field and is not available to display data (it appears blank). In the original models of the 3270, this byte was sufficient to store all of the display characteristics. In later models, which have more types of display characteristics, the additional information is kept in an area of buffer storage not associated with a fixed position on the screen. See Display characteristics for more about display characteristics.
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