base module 16 the data and communications module 55 as a representative module featuring the attachment to the base module 16 has a plurality of laterally disposed latching hooks or latch hooks 56 which become engaged by respective latching seats or latch seats 57 disposed along the adjacent edge of the base module 16 when the module 55 is moved toward and into engagement with the adjacent edge and then toward the battery compartment 44 as shown by the arrow electrical communication is established via a power and communications connector 61 the pins of which engage a mating connector socket 62 within the base module 16 a set of screws 63 may be tightened through the battery compartment 44 into a set of threaded seats 64 disposed in the adjacent wall of the module 55 to securely retain the attached module as an integrated part of the data terminal 10 at the top end of the data terminal 10 a lip or extending stop edge 66 of the module 55 engages a complementarily shaped seat 67 at the top end of the base module 16 to securely interlock the data and communications module 55 with the base module 16 it is contemplated for example for the module 55 to include any of a number of combinations of diverse functional elements for example the module 55 may include the aforementioned transceiver though the.