Abstract: An electronic keyboard musical instrument is operated by a main system computer in a manner dependent on the settings of input elements. A plurality of tone modules are used, each of which comprises a subsystem computer including a subsystem bus, a memory and a microprocessor. Data is exchanged between the main system computer and a subsystem computer through a bus switch which alternately connects the subsystem memory with the main system bus and the subsystem bus. This allows for an effectively "real time" exchange of data between the main system and the subsystem.

Abstract: An electronic musical instrument has input elements such as tone selector keys and control knobs which send input signals representing desired tone parameters to a primary computer. The primary computer, which includes a primary microprocessor and a primary memory, is connected with several voice modules and several effect-producing modules by means of a primary bus. Each voice module has a plurality of tone outputs for generating different tones. The tones for each voice module are produced by a respective subsystem including an auxiliary microprocessor, a clocking device and a digital-analog converter unit which are connected by an auxiliary bus. The auxiliary bus is connected with the primary bus via a bus switch. An auxiliary memory belonging to the subsystem is connected with the bus switch which permits the auxiliary memory to alternately communicate with the primary bus and the auxiliary bus.