MPUs and MCUs
How smart peripherals help automate low-level tasks in microcontroller systems
By Graeme Clark, principal product marketing specialist, Renesas Electronics T
he Renesas RA family of Arm Cortex based microcontrollers builds on Renesas’ rich history of microcontrollers such as the H8 and M16C families. The RA family enhances the peripheral functions that were originally implemented on these devices. These peripherals have been tried and tested over many years and provide proven and predictable operation, improve performance and reduce power consumption. In this article we’ll look at how these peripherals can be combined to automate low-level tasks found in a typical application.
The least understood peripheral found on the RA family is the Data Operations Circuit (DOC). This is a simple Arithmetic Logic Unit (ALU) that can offload simple tasks from the CPU, improving the response time and potentially reducing power consumption. The DOC has three basic functions: a 16-bit data comparison, a 16-bit addition, and a 16-bit subtraction. The DOC can be used by transferring the required data using a DMA controller or the Data Transfer Controller (DTC) as shown in Figure 1. When using the 16-bit comparison mode, an initial reference value is loaded into the DOC. The data to be compared is then loaded and compared with a reference value. The DOC can generate an interrupt on match true or match false.
When using the 16-bit addition mode, an initial value is loaded. Additional 16- bit values are then loaded (one or more) and added to the original value. When all the required values are loaded, the count is checked for overflow, and an interrupt generated if required. This simple mechanism allows a decision to be made if a specific threshold value has been exceeded, which is ideal for applications like level sensing using the ADC.
Using the 16-bit subtraction mode, an initial value is loaded into the DOC.
36 April 2023 Components in Electronics
www.cieonline.co.uk Figure 1:
Simplified block diagram of the Data Operating Circuit (DOC)
Additional values are then loaded and subtracted from the original value. When all the values are loaded, the count is checked for underflow, and an interrupt generated if required.
The true power of the Data Operation Circuit is that it can be used to make logical decisions as to how the system will operate, without any CPU intervention. When combined with peripherals such as the
Direct Memory Access Controller (DMAC) or the Data Transfer Controller (DTC), the DOC becomes capable of making decisions based on data from almost any source. This is done without CPU intervention, even
Figure 2: Simplified
diagram of the RA interrupt controller
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