Browse Prior Art Database

Time Independent Microcode

IP.com Disclosure Number: IPCOM000043072D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Wallace, LJ: AUTHOR

Abstract

An improved microcode architecture is disclosed which has been used for the IBM 4720 matrix printer. Instead of using an electromechanical emitter or a fixed frequency clock for generating print wire fire timing interrupts and print head carrier step motor interrupts, a programmable timer under control of a microprogram is used to permit a single interrupt to be presented after a different time delay to print different fonts at various print densities. This removes the need for the microprocessor to generate the varying time intervals by designing the length of the various microcode instruction paths to be the exact length required for the time period needed by the mechanical hardware.

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Time Independent Microcode

An improved microcode architecture is disclosed which has been used for the IBM 4720 matrix printer. Instead of using an electromechanical emitter or a fixed frequency clock for generating print wire fire timing interrupts and print head carrier step motor interrupts, a programmable timer under control of a microprogram is used to permit a single interrupt to be presented after a different time delay to print different fonts at various print densities. This removes the need for the microprocessor to generate the varying time intervals by designing the length of the various microcode instruction paths to be the exact length required for the time period needed by the mechanical hardware. The microcode responds to an interrupt to perform a wire fire and then does all of the processing necessary in preparation for the next wire fire including setting the different time delay, as necessary, to control both the print head step motor and wire fire, whichever is the next required action. In prior-art printers, the carriage control escapement or step motor was designed to have proper increments for ten pitch or twelve pitch character spacing. Often different mechanical escapement racks were provided for each pitch or, alternately, different electromechanical emitter pulses were provided for each of the print pitches to be printed. When microcomputers were employed to perform the print logic functions, these microcomputers could be programmed to provide the timing pulses necessary to control both the print head carrier step motor and the print wire fire pulses. The number of motor steps usually was required to be in a reasonably simple relationship with the number of picture elements in each character so that the print head motion control and wire fire logic did not get too complicated. Therefore, when a large number of different print pitches must be printed by the same printer, different microprograms were often required to provide the specialized timing relationships required. The improved architecture of this disclosure uses a programmable timer which can be set by the microprogram to provide an interrupt after a variable time delay determined by the microprogram. When the interrupt is received, the next function to be executed, e.g., step the print head carrier step motor or fire a wire, is executed by reference to a sequence table. This table also contains the time delays to be set into the programmable timer. After performing the actions to be taken, the pointer to the table is incremented so that the next interrupt will point to the next mechanical actions to be executed. After updating the interrupt pointer, other processing can be accomplished, such as receiving data from a communication line or converting the code of a character to be printed into the next slice of picture elements to be printed. When the processing has been completed or when the time for the next mechanical execution draws near, the pr...