Apparatus and method for improvement of communication between an emulator unit and a host device

In order to reduce the traffic over the communication bus (31) between the host processing unit (32) and an emulator server unit (34) during the test of a target processing unit (36), the commands are divided into groups of test commands. A group of commands is transferred to the emulator server unit (34) and stored in a memory unit (344) of the emulator server unit (34). The emulator server unit (34) then applies each command of the group of commands to a target processing unit (36). The resultant data generated as a result of the application of each command is stored in the emulator server unit (34). When all the commands of the group of commands have been executed by the target processing unit (36) and the resultant data stored in the emulator server unit (34), the resultant data is transferred to the host processing unit (32) in a single communication bus access.