CE97088 – PSoC® 4 ADC to PWM DMA Transfer Objective This code example demonstrates how to set up a PSoC® 4 direct memory access (DMA) channel to transfer data from the ADC peripheral to the PWM. Overview This code example demonstrates a peripheral-to-peripheral data transfer using PSoC 4 DMA. The DMA transfers the ADC result data to a PWM compare register. The change in ADC value creates a change in PWM duty. The transfer is triggered on each ADC end of conversion (EOC). This example is a use case of the “Single data element per trigger” mode. Requirements Tool: PSoC Creator™ 3.2. Associated Parts: PSoC 4200M and PSoC 4100M Related Hardware: CY8CKIT-044 Design Every DMA channel in PSoC 4 has two descriptor structures. The descriptor comprises information regarding the source and destination address, the modes of transfer, and other specifics related to a transfer. You can choose to use one or both of the descriptors in the channel. Refer to the DMA Component datasheet for more details on the use of descriptors. In this code example, a single DMA channel is configured with a single descriptor, which has the source address as the ADC result register and the destination as the PWM compare register. The trigger (tr_in) for the DMA is the ADC EOC. The transfer mode is set as “Single data element per trigger,” which results in the ADC result being transferred to the PWM compare register every time the EOC is asserted. Figure 1 illustrates the concept of this code example. Figure 1. ADC-to-PWM DMA Transfer DMA Channel ADC 2 bytes 2 bytes PWM EOC tr_in Descriptor 0 The SAR ADC is set up to run at 218 sps and with a resolution of 12 bits. The PWM is implemented using the TCPWM and is clocked at 12 MHz. The period of the PWM is selected to match the resolution of the SAR ADC. The sample rate of the SAR ADC is selected as very slow, compared to the PWM frequency. Figure 2 shows the DMA Component configuration. www.cypress.com Document No. 001-97088 Rev. ** 1 PSoC® 4 ADC to PWM DMA Transfer 1. The ADC result and the PWM compare register are both addressed as 32-bit registers in PSoC 4. Hence the Data element size in the DMA configuration is set as 4 bytes. Though the relevant bits in the registers are only the lower 16 bits, the transfer needs to be 32 bits since 16-bit accesses from the peripheral registers are not supported. 2. The descriptor is configured to transfer one data element before being considered complete. The next EOC retriggers the DMA channel and the descriptor for another single-element transfer. 3. The Transfer mode is selected as a “Single data element per trigger.” This means that one data element (a 32-bit word) is transferred from the ADC to the PWM compare register each time the trigger (ADC EOC) is asserted. Figure 2. DMA Configuration 1 2 3 The only code required for the DMA is to call the Start routine, available in the Component application programming interface (API). The start function has source and destination addresses as parameters for the transfer. DMA_1_Start((void*)ADC_SAR_Seq_SAR_CHAN0_RESULT_PTR,(void*)PWM_COMP_CAP_PTR); The register names for the ADC result and PWM compare registers are located in the “Register” section of the corresponding Component datasheets. The Registers Technical Reference Manual (TRM) includes the register names and addresses. The source and destination addresses can also be set using the API functions DMA_SetSrcAddress() and DMA_SetDstAddress(). Design Considerations No additional code is required after the DMA initialization, when the CPU is free to do other tasks. The DMA can function in the PSoC 4 Sleep mode, so you can put the device to sleep after initialization to reduce system power consumption. Note When the voltage on the ADC is close to zero, there is a chance that the ADC result will go negative due to a negative offset. This can create an unexpectedly large PWM duty cycle. www.cypress.com Document No. 001-97088 Rev. ** 2 PSoC® 4 ADC to PWM DMA Transfer Hardware Setup The hardware setup explained in this section is for use with the CY8CKIT-044. Figure 3 shows the project schematic. Input setup: Connect a voltage between Vdd and GND to P2[0], for example, using a potentiometer or signal generator. Output setup: The PWM output is already connected to pin P0[6], which connects to the Red LED on CY8CKIT-044. Figure 3. Project Schematic Operation Changing the input voltage will change the brightness of the Red LED on the CY8CKIT-044. Note When the voltage on the ADC is close to zero, there is a chance that the ADC result will go negative due to a negative offset. This will cause the LED to step to very high brightness when the input voltage is very close to zero. Components Table 1 lists the PSoC Creator Components used in this example, as well as the hardware resources used by each. The DMA Component settings are shown in Figure 2. Table 1. PSoC Creator Components Component or User Module Hardware Resources ADC_SAR_SEQ SAR ADC DMA 1 DMA channel PWM TCPWM www.cypress.com Document No. 001-97088 Rev. ** 3 PSoC® 4 ADC to PWM DMA Transfer Related Documents Table 2 lists the relevant application notes, code examples, knowledge base articles, device datasheets, and Component datasheets. Table 2. Related Documents Application Notes AN79953 – Getting Started with PSoC 4 Introduces you to PSoC 4, an ARM® Cortex™-M0 MCU based programmable system-on-chip. It helps you explore the architecture and PSoC Creator development tools. Code Examples CE95351 – Fixed Function PWM with PSoC 4 CE95275Sequencing SAR ADC and Die Temperature Sensor with PSoC 4 CE95272 – SAR ADC in Differential Mode using Pre-Amplifier with PSoC 4 PSoC Creator Component Datasheets PSoC 4 Sequencing Successive Approximation ADC (ADC_SAR_Seq ) PSoC 4 Timer Counter Pulse Width Modulator (TCPWM) Device Documentation PSoC 4 Datasheets PSoC 4 Technical Reference Manuals Development Kit (DVK) Documentation CY8CKIT-044 – PSoC 4 M-Series Pioneer Kit For questions or suggestions on this code example please contact [email protected]. www.cypress.com Document No. 001-97088 Rev. ** 4 PSoC® 4 ADC to PWM DMA Transfer Document History Document Title: CE97088 - PSoC® 4 ADC to PWM DMA Transfer Document Number: 001-97088 Revision ECN ** 4866747 www.cypress.com Orig. of Change QVS Submission Date 08/13/2015 Description of Change New code example. Document No. 001-97088 Rev. ** 5 PSoC® 4 ADC to PWM DMA Transfer Worldwide Sales and Design Support Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find the office closest to you, visit us at Cypress Locations. PSoC® Solutions Products Automotive cypress.com/go/automotive psoc.cypress.com/solutions Clocks & Buffers cypress.com/go/clocks PSoC 1 |PSoC 3 | PSoC 4 |PSoC 5LP Interface cypress.com/go/interface Lighting & Power Control cypress.com/go/powerpsoc cypress.com/go/plc Memory cypress.com/go/memory PSoC cypress.com/go/psoc Touch Sensing cypress.com/go/touch USB Controllers cypress.com/go/usb Wireless/RF cypress.com/go/wireless Cypress Developer Community Community | Forums |Blogs | Video |Training Technical Support cypress.com/go/support PSoC is a registered trademark and PSoC Creator is a trademark of Cypress Semiconductor Corp. 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The inclusion of Cypress’ product in a life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. Use may be limited by and subject to the applicable Cypress software license agreement. www.cypress.com Document No. 001-97088 Rev. ** 6