A battery powered, portable, hand-held data terminal (10) of modular structure includes a base module (16, 136) with a keyboard (18) and a display screen (19) and their respective electrical functions (167, 164). A data and communications module may be selected from a number of different data and communications modules (48, 55, 75, 135) each having different types of data communications transceiver, or including in addition data collection devices, such as shelf label readers or bar code readers (76). The base module (16, 136) includes a microprocessor-controlled data communications and control interface having a predetermined protocol. To adapt the various type of data and communications modules for selection of any one thereof to become attached to the base module and function therewith, each of the data and communications modules includes a microprocessor (125, 144) operable to function as an emulator to interact with the microprocessor of the base module (16, 136).