DDR SDRAM and the TM-4
#DDR SDRAM
#memory subsystem
#RAM
#memory organization
#data bandwidth
#dynamic RAM
#computer interface
#high-speed memory
#memory access
#TM-4
Description: DDR SDRAM is a dynamic RAM standard designed to provide high memory depth and bandwidth. This section will present the essential DDR SDRAM background necessary for effective utilization of the TM-4's memory subsystem. It will cover memory organization and detail how both read and write operations are performed. In a DDR DRAM DIMM, there are typically two memory chips connected in parallel, with only their chip enable signals being unique. This configuration allows the two chips to share address and data lines. By selectively asserting only one chip enable signal at a time, this setup enables twice the memory depth compared to a single chip. The highest level of the memory addressing hierarchy controls these chip enable signals, referred to as chip selects. The remaining three addressing levels occur within a single memory chip. A simplified block diagram of the internals of a DDR SDRAM memory chip illustrates that at the core are four 2D memory array banks. Each memory bank is addressed by both a row and column address. To comprehend why this memory structure was chosen, it is necessary to understand the process of reading from one of the 2D memory arrays.
Reading from the 2D memory array involves several steps. The first step is selecting which row in the memory array to address, accomplished by issuing an ACTIVE command to the memory. This command results in the memory array outputting an entire row of data via the sense amplifiers. At this point, the memory chip is prepared to accept read commands, which include a column address that is decoded to select the specific piece of data currently outputted by the sense amplifiers. Once the transaction is completed, the 2D memory array can be returned to an idle state by issuing a PRECHARGE command to the memory. The necessity to both activate and precharge the 2D memory array implies that data cannot be transmitted on every clock cycle, as the memory bank is engaged in handling other tasks. To mitigate the time required for activation and precharging, DDR SDRAM memory chips feature four independent banks of memory. This design allows transactions to continue on the remaining banks while a particular bank is being activated or precharged.
The DDR SDRAM architecture is characterized by its ability to perform operations in a highly efficient manner, leveraging the parallelism offered by multiple memory banks. Each bank operates independently, which enhances throughput and minimizes latency during read and write operations. The ACTIVE command initiates a read cycle by activating a specific row in the selected memory bank, allowing the data to be accessed swiftly. After the data has been read, the PRECHARGE command is issued to prepare the bank for subsequent operations. This dual-command structure ensures that the memory can handle multiple requests effectively, thus optimizing performance.
In practical implementations, the DDR SDRAM memory subsystem is typically integrated into larger systems, such as computing devices, where high-speed data processing is critical. The ability to interleave operations across multiple banks allows for continuous data flow, which is particularly beneficial in applications requiring high bandwidth, such as graphics processing and high-performance computing. Additionally, the unique chip enable signals facilitate the scalability of memory configurations, enabling designers to create systems with varying memory capacities while maintaining efficient data access protocols. Overall, the DDR SDRAM standard serves as a cornerstone in modern memory technology, balancing complexity and performance to meet the demands of contemporary electronic systems.DDR SDRAM is a dynamic ram standard that is designed to provide high memory depth and bandwidth. This section will provide the basic DDR SDRAM background necessary to effectively use the TM-4`s memory subsystem. In particular the memory organization will be presented, followed by a description of how both reads and writes are performed.
In a DDR S DRAM dimm there are usually two memory chips connected in parallel, with only their chip enable signals being unique. This configuration allows the two chips to share address and data lines. By selectively asserting only one chip enable single at a time, this configuration allows twice the memory depth compared with only a signal chip.
The highest level of the memory addressing hierarchy controls these chip enable signals. This addressing level is called the chip selects. The remaining three addressing levels all take place within a single memory chip. Figure 1 shows a simplified block diagram of the internals of a DDR SDRAM memory chip. At the core of the memory chip are four 2D memory array banks. Each of these memory banks is addressed by both a row and column address. To understand why this memory structure was selected it is necessary to first understand the process of reading from one of the 2D memory arrays. To read from the 2D memory array involves several steps. The first step involves selecting which row in the memory array to address. This is accomplished by issuing an ACTIVE command to the memory. This results in the memory array outputing an entire row of data via the sense amplifiers, shown in figure 1.
At this point the memory chip is ready to accept read commands. These read commands include a column address, which is decoded and used to select which piece of data, currently outputted by the sense amplifiers, to read. Once the transaction is completed the 2D memory array can be returned to an idle state. This is accomplished by issuing a PRECHARGE command to the memory. The need to both activate and precharge the 2D memory array means that data can not be transmitted on every clock cycle, since the memory bank is busy handling other tasks.
In order to provide a method to mask the time required to activate and precharge the memory array, DDR SDRAM memory chips contain four independent banks of memory. The idea is that while a given bank is being activated or precharged, transactions can still occur on the remaining banks.
Reading from the 2D memory array involves several steps. The first step is selecting which row in the memory array to address, accomplished by issuing an ACTIVE command to the memory. This command results in the memory array outputting an entire row of data via the sense amplifiers. At this point, the memory chip is prepared to accept read commands, which include a column address that is decoded to select the specific piece of data currently outputted by the sense amplifiers. Once the transaction is completed, the 2D memory array can be returned to an idle state by issuing a PRECHARGE command to the memory. The necessity to both activate and precharge the 2D memory array implies that data cannot be transmitted on every clock cycle, as the memory bank is engaged in handling other tasks. To mitigate the time required for activation and precharging, DDR SDRAM memory chips feature four independent banks of memory. This design allows transactions to continue on the remaining banks while a particular bank is being activated or precharged.
The DDR SDRAM architecture is characterized by its ability to perform operations in a highly efficient manner, leveraging the parallelism offered by multiple memory banks. Each bank operates independently, which enhances throughput and minimizes latency during read and write operations. The ACTIVE command initiates a read cycle by activating a specific row in the selected memory bank, allowing the data to be accessed swiftly. After the data has been read, the PRECHARGE command is issued to prepare the bank for subsequent operations. This dual-command structure ensures that the memory can handle multiple requests effectively, thus optimizing performance.
In practical implementations, the DDR SDRAM memory subsystem is typically integrated into larger systems, such as computing devices, where high-speed data processing is critical. The ability to interleave operations across multiple banks allows for continuous data flow, which is particularly beneficial in applications requiring high bandwidth, such as graphics processing and high-performance computing. Additionally, the unique chip enable signals facilitate the scalability of memory configurations, enabling designers to create systems with varying memory capacities while maintaining efficient data access protocols. Overall, the DDR SDRAM standard serves as a cornerstone in modern memory technology, balancing complexity and performance to meet the demands of contemporary electronic systems.DDR SDRAM is a dynamic ram standard that is designed to provide high memory depth and bandwidth. This section will provide the basic DDR SDRAM background necessary to effectively use the TM-4`s memory subsystem. In particular the memory organization will be presented, followed by a description of how both reads and writes are performed.
In a DDR S DRAM dimm there are usually two memory chips connected in parallel, with only their chip enable signals being unique. This configuration allows the two chips to share address and data lines. By selectively asserting only one chip enable single at a time, this configuration allows twice the memory depth compared with only a signal chip.
The highest level of the memory addressing hierarchy controls these chip enable signals. This addressing level is called the chip selects. The remaining three addressing levels all take place within a single memory chip. Figure 1 shows a simplified block diagram of the internals of a DDR SDRAM memory chip. At the core of the memory chip are four 2D memory array banks. Each of these memory banks is addressed by both a row and column address. To understand why this memory structure was selected it is necessary to first understand the process of reading from one of the 2D memory arrays. To read from the 2D memory array involves several steps. The first step involves selecting which row in the memory array to address. This is accomplished by issuing an ACTIVE command to the memory. This results in the memory array outputing an entire row of data via the sense amplifiers, shown in figure 1.
At this point the memory chip is ready to accept read commands. These read commands include a column address, which is decoded and used to select which piece of data, currently outputted by the sense amplifiers, to read. Once the transaction is completed the 2D memory array can be returned to an idle state. This is accomplished by issuing a PRECHARGE command to the memory. The need to both activate and precharge the 2D memory array means that data can not be transmitted on every clock cycle, since the memory bank is busy handling other tasks.
In order to provide a method to mask the time required to activate and precharge the memory array, DDR SDRAM memory chips contain four independent banks of memory. The idea is that while a given bank is being activated or precharged, transactions can still occur on the remaining banks.