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Microprogramming

IP.com Disclosure Number: IPCOM000079522D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

McMahon, RF: AUTHOR

Abstract

A microprogrammed data-processing system has an addressable microprogram store 20, the addressing both selecting a microprogram instruction to be read out from the store and the format in which that instruction is to be read out. This reduces the number of microprogram instructions that are required to be stored.

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Microprogramming

A microprogrammed data-processing system has an addressable microprogram store 20, the addressing both selecting a microprogram instruction to be read out from the store and the format in which that instruction is to be read out. This reduces the number of microprogram instructions that are required to be stored.

The formatting logic is as shown. A microprogram instruction can be supplied to ISDR register 30 in STRAIGHT/REVERSED and/or TRUE/COMPLEMENT form depending on the bits in register 46, which effectively form part of the address of the microinstruction. The store 20 itself is conventionally addressed.

Instructions (shown as 4-bits long, but much longer in practice) are transmitted STRAIGHT (that is, unchanged) to AND circuits 60 via lines 61-64, and simultaneously in REVERSE format to AND circuits via lines 66-69. When the instruction is to be transmitted in its STRAIGHT format, a "1" bit in the left- hand position of the ASDR 46 will enable AND's 60 and block AND's 65 due to the inverter 71, while the REVERSE format, indicated by a "0" bit in the left-hand position of ASDR 46, will enable AND's 65 and block AND's 60. The instruction, in its STRAIGHT or REVERSE format, passes through OR's 70 to appropriate true/complement (T#C) circuitry 72, responsive to signals on line 73 from the right-hand bit of ASDR 46, which transmits the microinstructions to ISDR 30 in the appropriate format.

It will be observed that if microprogram instructions ar...