 This "Acorn Business Computer" (ABC) plan required a number of second processors to be made to work with the BBC Micro platform.In developing these, Acorn had to implement the Tube protocols on each processor chosen, in the process finding out, during 1983, that there were no obvious candidates to replace the 6502.Because of many-cycle uninterruptible instructions, for example, the interrupt response times of the Motorola 68000 were too slow to handle the communication protocol that the host 6502-based BBC Micro coped with easily.