Memory module with means for generating a control signal that inhibits a subsequent overlapped memory cycle during a reading operation portion of a reading memory cycle

• US 4,055,851 A
• Filed: 02/13/1976
• Issued: 10/25/1977
• Est. Priority Date: 02/13/1976
• Status: Expired due to Term

• Current Assignee: Digital Equipment Corporation (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Stewart, Robert E., Jenkins, Stephen R., Northrup, Thomas A.
• Primary Examiner(s): Thomas, James D.
• Application Number:
  US05/658,113
• Time in Patent Office: 620 Days
• Field of Search: 340/172.5, 340/173 R, 364/200, 364/900
• US Class Current: 711/167
• CPC Class Codes: G06F 12/0864 using pseudo-associative means, e.g. set-associative or hashing
• CPC Class Codes: G06F 13/4239 with asynchronous protocol

Abstract

A random access memory module for connection in a memory arrangement for a digital data processing system that additionally includes a high speed associative memory unit. The associative memory unit contains a multiple location address memory and a multiple location data memory wherein there is a correspondence between each address location and a data location. Each time a central processor in the system initiates a reading operation, it issues an address to define a data location. If the associative memory unit contains that address at a location in its address memory, it performs a reading memory cycle and transfers data from the corresponding location in the data memory directly to the central processor. On the other hand, if the associative memory does not contain that address, it initiates a reading memory cycle with the random access memory module. It is possible for the associative memory unit to request successive transfers with one or more memory modules on an overlapped basis. Each memory module performs two successive operations during each transfer: namely, a reading operation and a successive writing operation. Control circuitry in the memory module generates a BUS OCCUPIED signal during the time interval of a reading operation that occurs during a reading memory cycle that is used to transfer data to the associative memory unit. The BUS OCCUPIED signal is transferred back to the associative memory unit to inhibit the initiation of any successive overlapped memory cycle until the completion of that reading operation.

Claims

1. A random access memory module for connection over a bus to a digital data processing system that, for each of successive memory cycles including reading and writing memory cycles, initiates a data transfer by transmitting binary address signals and asynchronous control signals that include a starting control signal for initiating a data transfer with said memory module and a binary direction control signal for controlling the direction of the data transfer between said random access memory module and the digital data processing system, said random access memory module comprising:

A. addressable storage means for storing digital data in addressable storage locations therein,

B. address decoding means for producing an enabling signal when said address decoding means receives, from the digital data processing system, binary address signals that identify a said storage location in said addressable storage means, and

C. control means connected to said addressable storage means and said address decoding means, said control means including;

i. memory cycle control means responsive to the enabling signal and the starting control signal for producing a selected one of the reading and writing memory cycles, each said memory cycle including a reading operation during which digital data is retrieved from an identified one of said locations in said addressable storage means and a succeeding writing operation during which data is stored in said identified location in said addressable storage means,

ii. timing signal means for generating a timing signal that corresponds to the interval of a reading operation during the operation of said memory cycle control means,

iii. reading signal means for generating a reading signal in response to a state of the direction control signal that designates a transfer of digital data from said memory module to the digital data processing system, and

iv. means responsive to said timing signal means and to said reading signal means for transmitting to the digital data processing system a BUS OCCUPIED signal that is coterminous with the timing signal during a reading cycle, the BUS OCCUPIED signal inhibiting the initiation of any succesive memory cycles by the digital data processing system until the completion of a reading operation during a reading memory cycle and the termination of the BUS OCCUPIED signal.

2. A random access memory module as recited in claim 1 wherein said control means additionally includes:

v. means for transmitting a START DELAY signal that initiates the memory cycle at said random access memory module, said START DELAY signal transmitting means being responsive to the asynchronous control signals it receives from the digital data processing system, and

vi. means connected to said START DELAY signal transmitting means and said BUS OCCUPIED signal transmitting means for transmitting an ACKNOWLEDGEMENT signal in response to the START DELAY signal, the ACKNOWLEDGEMENT signal being inhibited by the BUS OCCUPIED signal.

3. A random access memory module as recited in claim 2 wherein:

A. said addressable storage means comprises a plurality of random access memory stacks, each said stack containing a number of locations that are identified by a block of consecutive memory addresses, certain of said stacks having first memory cycle operating characteristics and the others of said stacks having second memory cycle operating characteristics, each said memory stack having means for generating a stack signal that identifies its corresponding memory cycle operating characteristic, and

B. said control means additionally comprises;

vii. means for receiving the stack signals from said memory stacks; and

viii. means responsive to the stack signals and the ACKNOWLEDGEMENT signal for generating a stack characteristic signal that corresponds to the stack signal of the stack identified by the binary address signals, said control means altering the timing of said BUS OCCUPIED signal in response to the stack characteristic signal.

4. A random access memory module as recited in claim 3 wherein said memory stacks are groups in pairs of stacks, said control means additionally including:

ix. means responsive to the stack signals from said memory stacks for generating an error signal that disables said START DELAY signal transmitting means when the stack signals indicate that each stack in a said pair have different memory cycle operating characteristics.

5. A random access memory module as recited in claim 1 wherein the digital data processing system transmits binary margin signals for establishing the values of analog control signals, said random access memory module additionally comprising means for converting the binary margin signals received from the digital data processing system to analog control signals and control circuit means for controlling operations of said addressable storage means in response to the analog control signals.