Zenith Electronics Corporation

Zenith Radio Corporation

Charles A Krause

Babu Rajaram

Randy J Vander Heyden

Barry A Watzman

In a dual microprocessor system, a processor transfer, or swap, arrangement and method therefor are disclosed for transferring control from one processor to another. The present invention involves the temporary suspension of operation of a first microprocessor which relinquishes system control and the initiation of operation of a second microprocessor which may begin operation either where it last left off or may execute a new operating routine in accordance with instructions provided by the first microprocessor. Provision is made for automatically handing over system control to the second microprocessor upon the occurrence of an interrupt. In addition, the microprocessor not exercising system control is rendered unresponsive to the occurrence of a program interrupt allowing it to continue opration unaffected by the program interrupt following its reactivation. -

Switchcover means and method for dual mode microprocessor system

In a video display system having a video random access memory (RAM) including a plurality of color memory banks, with one memory bank for each of the primary colors, provision is made for simultaneously writing to all of the color banks. A central processor unit (CPU) places data onto the system bus and asserts WRT-R, WRT-G and/or WRT-B signals in selectively writing at the same time to any or all of the video RAM banks, where the primary colors are red, green and blue. Logic circuitry coupled to the three RAM banks then gates designated Row and Column Address Strobe (RAS and CAS) signals to each of the color arrays followed by color video data signals. The time required to thus write video display information into the multi-bank video RAM array is thus reduced and system video data throughput correspondingly increased.

Multi-bit write feature for video RAM

A multi-key keyboard is scanned at high speed in such a manner as to substantially reduce erroneous key entries caused by the simultaneous engagement of more than one key. A keyboard processor determines which key is down by sequential scanning of the keyboard, encodes the selected key and sends this code to a master processor, or CPU. A 2-key lockout scanning approach is employed wherein keyboard scanning stops when two keys are selected simultaneously. Scanning is resumed when either one or both of the first two keys are released. By limiting simultaneous key engagement detection to two keys, system complexity and cost are kept within reasonable limits while insuring against erroneous key entries. Detecting and storing the key engagement sequence permits a selected special function, e.g., automatic key repeat, to be applied to the last selected key rather than to an earlier selected, but simultaneously engaged, key.

Keyboard scanning

A video display system utilizes three banks of memory for producing an 8-color or an 8-level gray scale display. A separate memory plane, or random access memory (RAM) array, for each of the 'primary' video colors, i.e., red, green and blue, is used in a bit-mapped video graphics implementation for a computer driven video display. In a monochrome display, pixel mixing produces the 8-level gray scale display. Each of the video planes may be selectively disabled as desired for special applications. For example, a limited animation capability may be provided by displaying one page while generating a new page in a non-displayed page. By disabling the currently displayed plane as the new plane is enabled, instantaneous page modification may be closely simulated for animated applications. The thus disabled video plane may then be used as any normal page of RAM for any other application. In addition, all of the video RAM planes may be disengaged from the central processing unit (CPU) to blank the video display for various applications such as during initial system reset or as part of an operating program.

Growing community of inventors

Stevensville, MI, United States of America

Charles A Krause