Multicasting system for selecting a group of memory devices for operation

• US 5,860,080 A
• Filed: 03/19/1996
• Issued: 01/12/1999
• Est. Priority Date: 03/19/1996
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Stone, Glen D., James, David V.
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): NGUYEN, THAN VINH
• Application Number:
  US08/618,628
• Time in Patent Office: 1,029 Days
• Field of Search: 711/1, 711/3, 711/4, 711/5, 711/111, 711/101, 711/112, 395/200.5, 370/401, 370/390, 370/408, 370/452
• US Class Current: 711/4
• CPC Class Codes: G06F 12/0669 with decentralised address assignment

Abstract

A system and method for multicasting control signals to selectively operate one memory device or groups of memory devices comprises a memory controller coupled to a plurality of memory devices by a command bus and a data bus. Each of the plurality of memory devices has a unique identification number. The system provides an addressing scheme in which an individual memory device or groups of memory device can be selected for operation by addressing the devices with a command packet. The memory controller broadcasts a command packet over the command bus to the plurality of memory devices. The packet includes an identification number. At each of the memory devices, selection logic is included to make the memory device operational if the identification number in the packet matches the identification number assigned to the memory device. The address in the packet is preferably encoded such that identification number has the same size regardless of whether a single memory device is being selected for operation or a group of memory devices are being selected for operation. The present invention also includes a method for selecting groups of memory devices for operation by multicasting a select address comprising the steps of: providing an memory identification number to each memory device, transmitting an memory device selection address, comparing the memory device selection address to the memory identification number, and asserting a signal to make the memory device operational if the memory device selection address and the memory identification number match.

Claims

1. In a system having a memory controller coupled by a bus to a plurality of memory devices, a method for activating a group of memory devices for operation, the method comprising the steps of:

providing a unique memory identification number for each memory device;

transmitting, from the memory controller to the plurality of memory devices, a packet including an encoded memory device selection address identifying the group of memory devices, the group including at least two memory devices and less than the entire plurality of memory devices, and a command;

comparing the encoded memory device selection address to the memory identification number at each one of the plurality of memory devices; and

enabling operation of each memory device where the memory identification number matches the memory device selection address to perform the command at the group of memory devices.

2. The method of claim 1 wherein step of providing comprises the step of storing the memory device selection address at the memory device prior to and for use in the comparing step.

3. The method of claim 1 wherein the step of providing an unique memory identification number for each memory device further comprises the steps of:

successively transmitting on the bus a series of unique identification numbers;

transmitting an initialization signal from the memory controller to a first memory device of the plurality of memory devices and then successively to each remaining memory device of the plurality of memory devices; and

storing a unique identification number pre sent on the bus as the memory identification number for each memory device when the initialization signal is received.

4. The method of claim 1 wherein the step of transmitting a memory device selection address from the memory controller to the plurality of memory devices further comprises the steps of:

transmitting an identification number on the bus;

transmitting a command on the bus; and

transmitting an address on the bus.

5. The method of claim 1 wherein the memory device selection address is encoded such that the number of memory devices in the group is two, four, eight or sixteen memory devices.

6. The method of claim 1 wherein the comparing step is performed by more than two memory devices, and wherein more than two memory devices are made operational.

7. A memory system providing activation of a group of memory devices for operation, the system comprising:

a first bus for transmitting commands and addresses;

a second bus for transmitting data;

a first memory device for storing data having a control input and a bi-directional port, the control input of the first memory device coupled to the first bus, the bi-directional port of the first memory device coupled to the second bus, the first memory device being selectively operable in response to a signal receive at the control input;

a second memory device for storing data having a control input and a bi-directional port, the control input of the second memory device coupled to the first bus, the bi-directional port of the second memory device coupled to the second bus, the second memory device being selectively operable in response to a signal received at the control input; and

a memory controller having a first output and a bi-directional port, the first output of the memory controller coupled to the first bus and the bi-directional port of the memory controller coupled to the second bus, the memory controller for providing addresses and command to selectively operate one from the group of the first memory device, the second memory device and both the first and second memory devices.

8. The system of claim 7 wherein the first bus comprises a plurality of data signal lines, a clock signal line and a flag signal line, the flag signal line being used to indicate transmission of a command packet from the memory controller to the first and second memory devices.

9. The system of claim 7 wherein the memory controller creates and transmits a command packet including a memory device identification number, a command and at least one address.

10. The system of claim 7 wherein:

the memory controller has an initialization output and an initialization input, and provides an initialization signal for loading unique identification numbers into the first and second memory devices;

the first memory device has an initialization output and an initialization input, the initialization input of the first memory device coupled to the initialization output of the memory controller, the first memory device storing data at the control input of the first memory device as a first memory device identification number in response to the initialization signal at the initialization input of the first memory device; and

the second memory device has an initialization output and an initialization input, the initialization input of the second memory device coupled to the initialization output of the first memory device, the initialization output of the second memory device coupled to the initialization input of the memory controller, the second memory device storing data at the control input of the second memory device as a second memory device identification number in response to the initialization signal at the initialization input of the first memory device.

11. The system of claim 7 further comprising:

a third memory device for storing data having a control input and a bi-directional port, the control input of the third memory device coupled to the first bus, the bidirectional port of the third memory device coupled to the second bus, the third memory device being selectively operable in response to a signal received at the control input; and

wherein the memory controller selectively operates one from the group of the first memory device, the second memory device, the third memory device, the first and second memory devices, the first and third memory devices, the second and third memory devices or the first, second and third memory devices.

12. The system of claim 7 further comprising a buffer having an input and an output, the input of the buffer coupled to the first bus and the output coupled to the control input of the third memory device, the control input of the second memory device, and the control input of the third memory device.

13. The system of claim 7 wherein the first and second memory device each comprise:

a memory having control inputs and a data port for storing data, the data port of the memory device coupled to the second bus;

an identification register having an output and storing a unique memory device number;

a comparator having a first input, a second input and an output for comparing addresses, the first input of the comparator coupled to the output of the identification register, the second input of comparator coupled to the first bus; and

control logic having a select input, control input and outputs, the control logic decoding command and address information and selectively operating the memory device in response to a signal at the select input, the select input coupled to the output of the comparator, the control inputs coupled to the first bus, and the control outputs coupled to the control inputs memory device.

14. The system of claim 13 further comprising initialization logic providing a output coupled to a control input of the identification register for loading a unique identification number into the identification register.

15. The system of claim 13 wherein the control logic includes buffers and combinational logic necessary to decode a packet formed of a plurality of bytes sequentially transmitted over the first bus.

16. The system of claim 13 wherein the comparator includes combinational logic coupled such that the comparator will assert an internal chip select signal when the signal on the first bus is one of group of addresses that matches a value stored in the identification register.

17. An apparatus for storing data in a multicasting memory addressing system, the apparatus comprising:

memory device having control inputs and a data port for storing data, the data port of the memory device coupled to the second bus;

an identification register having an output and storing a unique memory device number;

a comparator having a first input, a second input and an output for comparing addresses, the first input of the comparator coupled to the output of the identification register, the second input of comparator coupled to the first bus; and

control logic having a select input, control input and outputs, the control logic decoding command and address information and selectively operating the memory device in response to a signal at the select input, the select input coupled to the output of the comparator, the control inputs coupled to the first bus, and the control outputs coupled to the control inputs memory device.

18. The apparatus of claim 17 further comprising initialization logic providing a output coupled to a control input of the identification register for loading a unique identification number into the identification register.

19. The apparatus of claim 17 wherein the control logic includes buffers and combinational logic necessary to decode a packet formed of a plurality of bytes sequentially transmitted over the first bus.

20. The apparatus of claim 17 wherein the comparator includes combinational logic coupled such that the comparator will assert an internal chip select signal when the signal on the first bus is one of group of addresses that matches a value stored in the identification register.