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Browse Prior Art Database

Branch On O-Register Control Word

IP.com Disclosure Number: IPCOM000048850D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Lemaire, CA: AUTHOR [+2]

Abstract

In a microcoded computer system such as the IBM System/38, control words are executed out of control storage 10 (Fig. 1) to interpret higher level instructions. System performance can be improved by reducing the number of control word execution cycles required to perform bit decoding. The branch on O-Register control word saves execution cycles for performing extended Op code decoding, multiple bit decoding, and table look-up functions. Control words (Fig. 1) are taken from control storage 10 at location addressed by control store address register (CSAR) 15 and are entered into control store operation register (CSOR) 20. The control words. including the branch on O-Register control word (Fig. 2), include bits for forming the next address by the next address generation logic 30 (Fig. 1).

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Branch On O-Register Control Word

In a microcoded computer system such as the IBM System/38, control words are executed out of control storage 10 (Fig. 1) to interpret higher level instructions. System performance can be improved by reducing the number of control word execution cycles required to perform bit decoding. The branch on O-Register control word saves execution cycles for performing extended Op code decoding, multiple bit decoding, and table look-up functions. Control words (Fig. 1) are taken from control storage 10 at location addressed by control store address register (CSAR) 15 and are entered into control store operation register (CSOR) 20. The control words. including the branch on O-Register control word (Fig. 2), include bits for forming the next address by the next address generation logic 30 (Fig. 1). The branch on O-Register control word uses bits from O- Register 50 to form part of the address for addressing the next control word.

O-Register 50 receives the results from Arithmetic and Logic Unit (ALU) 40. Hence, O-Register 50 stores the results of the ALU operation of the control word executed just prior to the branch on O-Register control word. Because the branch on O-Register control word uses the O-Register results of the previous control word, the bits to be tested need not be loaded into one of the machine registers 60. In most instances the desired bits to be tested are in the O-Register after execution of some particular control word, thus eliminating the time required for a separate operation to load the O-Register with data bits to be decoded.

In Fig. 3, it is seen that bits 4-9 and 10-13 of the branch on O-Register control word are entered into CSAR 15 as bi...