Data processing apparatus for controlling reading out of operands from two buffer storages

A data processing apparatus for fetching an operand indicated by an instruction from a storage which includes a main storage and a buffer store which stores a copy of frequently used instructions and data stored in the main storage, comprising:

• (a) first and second buffer storages in said buffer store and each being independently accessible;
• (b) instruction means for decoding instructions received in sequence and for outputting for each instruction a fetch request and at least one operand address according to whether said instruction is a one-operand instruction or a two-operand instruction, including means responsive to a one-operand instruction for providing said operand address to said first buffer storage and responsive to a two-operand instruction for providing one operand address to said first buffer storage and another operand address to said second buffer storage;
• and
• (c) storage control means for controlling the sequence of operation of said instruction means, including means connected to said buffer store for supervising the busy/free status of each of said first and second buffer storages, means for transferring a re-request signal to said instruction means upon a condition that said first buffer storage is busy when the fetch request calls for a one-operand instruction or a condition that at least one of said buffer storages is busy when said fetch request calls for a two-operand instruction, and means for indicating a busy state of said buffer store during a predetermined cycle when said re-request signal is transferred to said instruction means;
• wherein said instruction means further includes means responsive to said re-request signal for outputting said fetch request and said operand address once again to said storage control means and said buffer store in the sequence of receipt of instructions for decoding by said instruction means.