CPEN 120 Embedded Systems Memory PDF

CPEN 120 – EMBEDDED SYSTEMS Topic 5 Embedded Systems Memory Intended Learning Outcomes: At the end of this topic, the student should be able to: 1. Identify different memory technologies and memory types used in the embedded...

CPEN 120 – EMBEDDED SYSTEMS Topic 5 Embedded Systems Memory Intended Learning Outcomes: At the end of this topic, the student should be able to: 1. Identify different memory technologies and memory types used in the embedded system development. 2. Explain different factors to be considered in the selection of memory for embedded systems Learning Discussions Embedded memory refers to storage devices used for storing binary information, such as programs (instructions) and data, and supplying this information to the Microprocessor (MPU) or Microcontroller (MCU) as needed. These storage devices may be integrated onto the same chip, as seen in microcontrollers, or exist as separate memory components connected via interfaces like buses or interconnects, as is common with microprocessors. In an embedded system, memory acts as a physical storage space for input and output data. It also holds intermediate data produced during program execution. The Microprocessor (MPU) or Microcontroller (MCU) accesses memory to fetch data and instructions, processes them, and stores the resulting output back into memory as required. Types of Memory in Embedded Systems As an embedded hardware engineer, it's important to understand the different types of memory used in embedded systems as shown in Figure 5-1. Memory Technologies ROM RAM FLASH EEPROM EPROM SRAM DRAM Figure 5-1: Types of Memory CEIT-DCEEE 1  CPEN 120 – EMBEDDED SYSTEMS Table 5-1 provides the various memory types used in embedded systems, highlighting their definitions, advantages, disadvantages, application. This helps you choose the right memory for your design and use resources efficiently to ensure the system works well. Each memory type's unique characteristics, such as speed, cost, programmability, and capacity, make it suitable for specific applications, enabling designers to balance performance, cost, and functionality in their embedded system designs. Table 5-1 : Memory Types used in Embedded System Memory Type Definition/ Advantages Disadvantages Application Properties SRAM (Static Volatile memory - Fast access time SRAM (Static Volatile memory RAM) storing data in RAM) storing data in flip-flops; data flip-flops; data remains as long remains as long as power is as power is supplied. supplied. DRAM (Dynamic Volatile memory - Lower cost-per- - Slower access Multimedia RAM) storing data in byte time due to devices, capacitors; refresh communication requires periodic requirement systems, data refreshing. storage, large memory requirements Masked ROM Non-volatile - Low production - Cannot modify Applications memory with cost for large contents after requiring preprogrammed quantities production permanent, contents unchangeable specified during data chip production. PROM Non-volatile, - Greater - One-time Applications (Programmable programmable flexibility programming requiring ROM) after compared to only customized, fixed manufacturing, Masked ROM data but cannot be reprogrammed (OTP). EPROM (Erasable Non-volatile, - Can be erased - Higher cost than Software PROM) reprogrammable and PROM development, memory erasable reprogrammed testing processes with UV light. multiple times EEPROM Non-volatile, - Byte-level - Erased one Storing code and electrically erasure and sector at a time, data, firmware, erasable, byte-by- reprogramming not byte-by-byte large storage byte - Precision control requirements programmable over memory memory. contents Flash Memory High-density, - High density - Erased one High-density, non-volatile - Low cost sector at a time, non-volatile memory with fast - Fast read access not byte-by-byte memory with fast read access and read access and electrical electrical reprogramming reprogramming capabilities. capabilities. CEIT-DCEEE 2  CPEN 120 – EMBEDDED SYSTEMS NVRAM (Non- Modified SRAM - Fast access time - Higher cost Storing critical Volatile RAM) that retains data - Retains data - Limited write data that must without power. during power loss cycles persist during power loss, backup systems Factors to Consider When Choosing the Right Memory Type for Your Embedded System 1. Access Time Access time measures how quickly memory can read or write data. Faster access speeds enhance system performance but often come with higher costs. SRAM provides the fastest access, while DRAM and flash memory have comparatively slower speeds. 2. Cost The cost of memory significantly affects the total cost of an embedded system. SRAM is the most expensive per byte, followed by EEPROM and flash memory. DRAM offers the lowest cost-per-byte, making it ideal for applications needing large memory capacities. 3. Data Retention Data retention refers to a memory’s ability to preserve data without power. Non-volatile memories like ROM and hybrid memory types retain data even during power loss. In contrast, volatile memories like SRAM and DRAM lose all stored data when power is removed. 4. Programming and Erasing Capabilities This factor involves how easily memory can be programmed, erased, and how many write/erase cycles it supports. ROM types like PROM and EPROM have limited reprogramming options, while hybrid memories like EEPROM and flash memory offer greater flexibility with electrical erasure and programmability. 5. Density and Capacity Memory density and capacity determine how much data the memory can store. Flash memory is known for its high-density storage at an affordable cost, making it suitable for systems requiring large storage. In contrast, SRAM provides lower density due to its higher cost per byte. CEIT-DCEEE 3  CPEN 120 – EMBEDDED SYSTEMS References: ▪ Shivu KV (2009). Introduction to Embedded Systems. Mc Graw Hill Education ▪ Vicky K. (July 9, 2023). What is Embedded Memory? https://embeddedhardwaredesign.com/what-is-embedded- memory/#Different_Types_of_Memory_in_Embedded_Systems CEIT-DCEEE 4