Memory cartridge and its memory control method

• US 5,430,681 A
• Filed: 07/05/1994
• Issued: 07/04/1995
• Est. Priority Date: 05/08/1989
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd., Hitachi Maxell Limited (Maxell, Ltd.)
• Original Assignee: Hitachi, Ltd., Hitachi Maxell Limited (Maxell, Ltd.)
• Inventors: Sugawara, Ken, Matoba, Mikio, Sasaki, Toshio, Kimura, Katsutaka, Shimohigashi, Katsuhiro, Sakairi, Shigeru
• Primary Examiner(s): Popek, Joseph A.
• Assistant Examiner(s): LE, VU ANH
• Application Number:
  US08/266,870
• Time in Patent Office: 364 Days
• Field of Search: 365/229, 365/222, 365/233.5, 365/226, 365/227, 365/194
• US Class Current: 365/222
• CPC Class Codes: G11C 11/406 Management or control of the refreshing or charge-regeneration cycles
• CPC Class Codes: G11C 11/4074 Power supply or voltage generation circuits, e.g. bias voltage generators, substrate voltage generators, back-up power, power control circuits
• CPC Class Codes: G11C 5/141 Battery and back-up supplies
• CPC Class Codes: G11C 5/143 Detection of memory cassette insertion or removal; Continuity checks of supply or ground lines; Detection of supply variations, interruptions or levels G11C5/148 takes precedence; Switching between alternative supplies G11C5/141 takes precedence
• CPC Class Codes: G11C 5/147 Voltage reference generators, voltage or current regulators; Internally lowered supply levels; Compensation for voltage drops G11C5/141 takes precedence
• CPC Class Codes: G11C 8/18 Address timing or clocking circuits; Address control signal generation or management, e.g. for row address strobe [RAS] or column address strobe [CAS] signals

Abstract

A memory cartridge having a plurality of dynamic memory units includes an access conversion circuit which converts a static access signal into its inverted signal and an access control circuit which controllably switches between a signal for refreshing each dynamic unit and a signal for external access. The memory cartridge also includes a power switching circuit which switches power from an internal power supply to an external power supply when the memory cartridge is mounted to an external device.

Claims

1. A semiconductor memory comprising:

a dynamic RAM having a refresh operation performed in response to receipt of a refresh signal;

refreshing means, coupled to said dynamic RAM, for generating said refresh signal for refreshing said dynamic RAM;

signal reception means for receiving an access signal from an external device;

access control means for controlling access to said dynamic RAM on the basis of said refresh signal received from said refreshing means and said access signal received from said signal reception means;

said access control means including arbitration means for setting a constant time period for read accessing, shifted a predetermined time from a refresh period corresponding to said refresh signal, when a read access signal from said external device is received during a refreshing time period in said dynamic RAM; and

connector means for providing said access signal from an external device to said signal reception means when the semiconductor memory is coupled to said external device.

2. The semiconductor memory as set forth in claim 1, further comprising mode switching means for supplying indication of switching between two or more operational modes having different peak values of current supplied to said dynamic RAM.

3. The semiconductor memory as set forth in claim 2, wherein said operational modes of the semiconductor memory include a wait operational mode and a normal operational mode, the number of cells selected for one refresh operation in said wait operational mode is set to be smaller than that in said normal operational mode.

4. The semiconductor memory as set forth in claim 2, wherein said operational modes of the semiconductor memory include a wait operational mode and a normal operational mode, and a refreshing interval in said wait operational mode is set to be shorter than a refreshing interval in said normal operation mode.

5. The semiconductor memory as set forth in claim 2, wherein said operational modes of the semiconductor memory include a wait operational mode and a normal operation mode, and a word line activation signal is provided for activating some of a plurality of divided word lines, and wherein a number of the plurality of divided word lines activated in said wait operational mode being less in number than that activated in said normal wait operational mode.

6. The semiconductor memory as set forth in claim 1, further comprising:

battery means for supplying power to said dynamic RAM; and

a power supply switching circuit, coupled to said battery means and said connector means, for supplying power to said dynamic RAM from said external device instead of from said battery means when the memory semiconductor is coupled to said external device through said connector means.

7. The semiconductor memory as set forth in claim 6, wherein:

said dynamic RAM includes a plurality of dynamic RAM chips, each dynamic RAM chip having

resistance means which is connected to a power supply of said external device and said battery means when the semiconductor memory is coupled to said external device, and which is also connected to a power input terminal of said dynamic RAM in series with said dynamic RAM; and

capacitance means connected to the ground and between a power input terminal of said dynamic RAM and said resistance means; and

said resistance means and said capacitance means smoothing a peak current in a refresh period supplied to said dynamic RAM.

8. The semiconductor memory as set forth in claim 1, further comprising change detection means for detecting a change in an address signal supplied from said external device when the semiconductor is connected to said external device.

9. The semiconductor memory as set forth in claim 1, wherein said access control means includes change detection means for detecting a change in an address signal supplied from said external device when the semiconductor memory is connected to said external device,

said access control means generating a DRAM access signal corresponding to logic level inversion of a memory access signal supplied from said external device to said dynamic RAM for a predetermined time duration on the basis of detection of change in said address signal.

10. The semiconductor memory as set forth in claim 9, wherein said access control means inverts a logic level of a memory chip select signal and a chip enable signal supplied from the semiconductor memory.

11. The semiconductor memory as set forth in claim 1, wherein said access control means comprises:

counter means for counting a clock signal supplied from said external device or from a clock generator of the semiconductor memory;

logic operation means for performing a logic operation on said access signal and an output signal of said counter means, wherein bits of said counter means are allocated to both of a duration allowing generation of an access enable signal and a duration allowing generation of refreshing enable signal; and

means for generating,

in response to receipt of a refreshing enable signal, the refreshing enable signal when values of said bits are allocated to said duration of allowing generation of a said refreshing enable signal, and,

in response to receipt of memory access signals, said access signals when the values of said bits are allocated to said duration allowing generation of said access enable signal.

12. The semiconductor memory as set forth in claim 1, wherein said arbitration means comprises:

counter means for counting a clock signal supplied from said external device or from a clock generator of said semiconductor memory;

wherein at least two digit bits of said counter means are allocated to a duration allowing generation of an access enable signal, a precharge duration for said access enable signal, a duration for generation of a refreshing enable signal, and a precharge duration for said refreshing enable signal; and

means for generating the refreshing enable signal and receiving memory access signals including a chip select signal and a chip enable signal when values of said two digit bits are allocated to said duration of generating the refreshing enable signal and for generating said access enable signal when values of said two digit bits are allocated to said duration of generating said access enable signal.

15. The memory semiconductor as set forth in claim 1, wherein said arbitration means enables one of said refresh signal and said access signal which has been provided earlier than the other and disables the other.

13. The method of controlling a semiconductor memory which requires a refreshing operation to store and hold data therein, wherein read access to the semiconductor memory is externally specified, comprising the steps of:

setting a read access duration having a predetermined time width which is shifted by a predetermined time from refreshing duration when said read access to said semiconductor memory is specified during a refreshing operation; and

latching a held data read out from the semiconductor memory in a latching circuit at the end of said set read access duration.

14. The method of controlling a semiconductor memory as set forth in claim 13, further comprising the step of setting a next refreshing duration following said set read access duration as delayed by a predetermined time from said set read access duration.