Abstract: In order to reduce the size of the memory employed to store firmware, the firmware is written in virtual control words which are then reduced by allotting them to a primary control word memory and at least one secondary control word memory which is addressed by a field in the primary control word memory. A virtual set of secondary control words are each divided into a plurality of fields, and each field of each secondary virtual control word is marked as guarded or "don't care". If a field is marked as "don't care", the function represented by the virtual control word will perform properly no matter what the content of that field. Virtual control word pairs are then examined to ascertain if they can be combined into a single control word.

Abstract: In order to efficiently undertake the micro-steps required to execute an extended instruction in a central processing unit, a main sequence controller and a separate basic operations controller having its own sequencer and the ability to run semi-autonomously are provided. Normally, the main sequence controller determines the operation of the basic operations controller, but, in the case of execution of, for example, a multi-word instruction requiring extended basic operations, the basic operations controller temporarily takes control over the main controller until the extended basic operations have been completed. The result is a relatively simple sequencer that supports tight micro-coded functions where many of the sequence decisions can be predetermined.

Abstract: Method and apparatus to reduce the number of control words stored in a read only control store of a microprogrammed unit of the CPU of a large scale computer. A set of control fields are required to control the active elements of the unit to cause the unit to execute a large number of different basic operations. Typically the required set of control fields are included in control words stored in a control store controlling the unit during the execution of a basic operation. Obtaining some of the set of required control fields from other sources available within the unit results in a significant reduction in the number of control words stored in the control store without reducing the functionality of the unit.

Abstract: In a central processor incorporating at least one co-processor, such as a floating point arithmetic co-processor, in addition to a basic arithmetic logic unit, the problem of rationalizing the contents of the accumulator and supplementary accumulator registers without the burden of speed penalties is addressed and solved. This is achieved by providing input/output access to a common register file and by switching control of the register file to the proper processing unit appropriately. A single, shared accumulator register and a single, shared supplementary accumulator register are included in the stack along with other sharable registers such as address modification registers. Thus, the contents of the accumulator register and the supplementary accumulator register are always up-to-date and available to all processing units in the central processor without the need for first carrying out rationalization steps.

Abstract: A call forwarding device includes a plurality of selectively interconnectable channel switches, each having a rotary port connected to a different outlet port of a telephone rotary switch and a modem port connected with a different modem of a facility answering site. An inbound call on any channel switch rotary port is initially directed to the modem port of the same channel switch for answer by the connected modem. If this modem fails to timely answer, the call is automatically re-routed internally of the answering site to the modem port of another, available channel switch for answer by its connected modem or is automatically re-routed to the rotary port of another, available channel switch and call forwarded externally to a backup answering site for answer by a modem thereat.