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Difference Between AHB and APB
AHB (Advanced High-performance Bus) and APB (Advanced Peripheral Bus) are two bus protocols that are extensively used in the design of complex digital systems.
The key difference between AHB and APB is their speed and intended usage. AHB is designed for high-performance applications requiring fast data transmission rates and low-latency communication, whereas APB is designed for slower peripherals not requiring high-speed data transport.
Read this article to find out more about AHB and APB and how they are different from each other.
What is AHB?
AHB is an ARM-designed high-performance bus protocol for connecting high- speed peripherals and memory in a system-on-a-chip (SoC) design. The AHB is a pipelined bus with separate address and data phases that allows high-speed data transmission between peripherals.
The bus matrix, master interface, and slave interface are the three major components of the AHB bus protocol. The bus matrix handles bus transaction arbitration and routing between master and subordinate peripherals. The bus master uses the master interface to start transactions on the bus, while slave peripherals use the slave interface to respond to transactions initiated by the master.
The AHB protocol supports burst transactions, which allow the transfer of multiple data items in a single transaction. This decreases the overhead of address and control signals, improving the bus's efficiency. The AHB also allows split transactions, which allow multiple transactions on the bus to overlap. This reduces the latency of the bus and improves system efficiency.
AHB can handle transfers ranging from single bytes to bursts of up to 16 beats. It also allows a variety of transfer modes, such as single transfer, incremental burst, and fixed burst. The AHB bus protocol is extremely configurable, allowing designers to optimize the bus's performance to their specific needs.
The AHB protocol has several key characteristics that make it ideal for high- performance applications. A high-speed clock rate, low-latency communication, and efficient data transfer methods are among them. The AHB bus protocol is commonly used in SoC designs for applications such as microcontrollers, DSPs, and multimedia systems.
What is APB?
APB (Advanced Peripheral Bus) is an ARM-designed low-power, low-cost bus protocol for connecting low-speed peripherals in a system-on-a-chip (SoC) design. The APB is a simple bus with a single clock edge protocol, making it simple to implement and lowering total system complexity.
The bus interface unit (BIU) and the peripheral bus interface (PBI) are the two primary components of the APB bus protocol (PBI). The BIU handles bus transaction arbitration and routing between master and subordinate peripherals. The slave peripherals use the PBI to respond to transactions started by the master.
The APB protocol has several key characteristics that make it ideal for low-speed peripheral applications. A low-power clock rate, low-complexity communication, and an easy data transfer mechanism are among them. The APB bus protocol is commonly used in SoC designs for microcontrollers, sensors, and networking devices.
The APB bus protocol is a single-clock edge protocol that simplifies peripheral design by removing the need for extra control signals. It uses separate address and data phases, similar to the AHB protocol, but at a slower clock rate. The APB protocol allows for both single and burst transfers, but not divided transactions.
APB supports a wide variety of transfer sizes, from single bytes to 256-byte bursts. It also allows a variety of transfer modes, including single and incremental transfers. The APB bus protocol is highly configurable, allowing designers to optimise the bus's performance to their particular requirements.
Difference between AHB and APB
The following table highlights the major differences between AHB and APB −
Characteristics |
AHB |
APB |
|---|---|---|
Definition |
AHB is an ARM-designed high-performance bus protocol for connecting high- speed peripherals and memory in a system-on-a-chip (SoC) design. |
APB is an ARM-designed low-power, low-cost bus protocol for connecting low-speed peripherals in a system-on-a-chip (SoC) design. |
Speed |
High |
Low |
Clock Rate |
100 MHz to 1 GHz |
10 MHz to 100 MHz |
Latency |
AHB latency is low. |
APB latency is high compared to AHB. |
Transfer Size |
The AHB transfer size is up to 16 beats. |
APB transfer size is up to 256 bytes. |
Modes of Transfer |
single, incremental, and fixed burst |
Single and incrementing transfers |
Power Consumption |
High |
Low |
Number of Pins |
Many |
Fewer |
Complexity of Signal |
AHB has a complex signal interface. |
APB has a simple signal interface. |
Conclusion
In conclusion, AHB and APB are two different bus protocols that are used in ARM-based system-on-a-chip (SoC) designs. The primary difference is that AHB is a high-performance bus used to connect high-speed components such as processors and memory, whereas APB is a slower bus used to connect slower peripherals such as GPIOs and timers.
AHB is designed for high-bandwidth applications requiring fast data transfer rates and low-latency communication, whereas APB is designed for slower peripherals not requiring high-speed data transport. The suitable bus protocol for a specific SoC design is selected based on the system's specific requirements and performance requirements. The decision between AHB and APB is determined by system design requirements such as data transfer rate, bus width, and power usage.
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