CCU Data Flow Controlled by Mixed Picocode/Hardware
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
To maintain the high performance level of a central control unit (CCU) controlled by control words in a read-only storage (ROS), a hardware control is available either to generate controls independently from the ROS for the first machine control word or to modify the ROS output word. Thanks to the hardware, the cycle time duration as well as the number of cycles necessary to perform the operation are decreased. The machine control word necessary for the first cycle of most of the instructions, i.e., A and B operand bus source gating, is generated without adding one CCU cycle. The general control logic flow is shown in Fig. 1. The register POP contains the instruction. Based on its decode, a ROS first address is generated and the ROS word is immediately latched in a "ROS output word" register.