The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 21, 1994
Filed:
Feb. 18, 1992
Miki Matsumoto, Ohme, JP;
Katsuyuki Sato, Akishima, JP;
Hitachi, Ltd., Tokyo, JP;
Abstract
A multi-port memory is provided which is capable of being backed up by a battery to provide a resume function for a digital processor. In a preferred embodiment, a resume function can be provided for a VRAM without restricting the bit rate of image data or the function of the frame memory. Preferably, the memory includes a memory array MARY of memory cells of stereoscopic structure. A high voltage VCH for word line selection can be generated by a voltage-doubling word boost circuit which has its boosting ratio switched stepwise in accordance with the potential of an internal supply voltage. Moreover, a substrate potential generator is provided which has a first substrate potential generator having a relatively low current supplying capacity, which is steadily brought into an operative state, and a second substrate potential generator having a relatively high current supplying capacity which is selectively brought into an operative state. During battery backup, the multi-port memory is in a self-refresh memory. Also, the number of memory mats to be simultaneously activated in the self-refresh mode is made larger than that in the ordinary mode, and a refresh timer circuit RTM for setting the refresh period is of a diffusion layer leakage type.