ADC Diagnostic Reference Conversion

This code example demonstrates the usage of the diagnostic reference for debugging the functionality of the on-chip ADC (Analog-to-Digital Converter) module.

Device

The device used in this code example (CE) is:

TRAVEO™ T2G CYT4BF Series

Board

The board used for testing is:

TRAVEO™ T2G evaluation kit (KIT_T2G-B-H_EVK, KIT_T2G-B-H_LITE)

Scope of work

In this example, the diagnostic reference module is used to provide a known voltage as an input to the ADC module. The purpose of this setup is to test the ADC's functionality. The output count of the ADC is converted to equivalent voltage. The ADC is working correctly, if the measured voltage matches the input voltage within an acceptable margin of error.

This approach can be used for debugging and testing purposes.

Introduction

SAR ADC
TRAVEO™ T2G features a successive approximation register analog-to-digital converter (SAR ADC), The SAR ADC is designed for applications that require a moderate resolution and high data rate. It consists of the following blocks:

SARADC Core
SARMUX
SAR sequencer
Diagnostic reference
Reference buffer

SARMUX is an analog multiplexer to connect the signal sources to the ADC input; SARADC core then performs analog-to-digital conversion. A SAR sequencer is responsible for prioritizing the triggers requests, enable the appropriate analog channel, and control the sampling.

TRAVEO™ T2G platform supports the following ADC features:

Three SAR A/D converters with up to 99 external channels
Each ADC supports 12-bit resolution and sampling rates of up to 1 Msps
Each ADC also supports six internal analog inputs like
- Bandgap reference to establish absolute voltage levels
- Calibrated diode for junction temperature calculations
- Two AMUXBUS inputs and two direct connections to monitor supply levels
Each ADC has a sequencer supporting autonomous scanning of configured channels
Synchronized sampling of all ADCs for motor-sense applications

SARMUX Diagnostics

SARMUX diagnostics is a functional safety feature, used to verify the connection from the selected SARMUX input to ADC sampling capacitor. This is accomplished by connecting only the diagnostic reference output to the selected SARMUX input.

The SARMUX diagnostics mode is an optional per channel feature, which is selected by setting the PASSx_SARy_CHz_SAMPLE_CTL.OVERLAP_DIAG field. The diagnostic reference can be configured by setting an appropriate value in the PASSx_SARy_DIAG_CTL.DIAG_SEL field to provide one of the following available reference voltages:

`0x0`	VREFL	DiagOut = VrefL (default)
`0x1`	VREFH_1DIV8	DiagOut = VrefH * 1/8
`0x2`	VREFH_2DIV8	DiagOut = VrefH * 2/8
`0x3`	VREFH_3DIV8	DiagOut = VrefH * 3/8
`0x4`	VREFH_4DIV8	DiagOut = VrefH * 4/8
`0x5`	VREFH_5DIV8	DiagOut = VrefH * 5/8
`0x6`	VREFH_6DIV8	DiagOut = VrefH * 6/8
`0x7`	VREFH_7DIV8	DiagOut = VrefH * 7/8
`0x8`	VREFH	DiagOut = VrefH
`0x9`	VREFX	DiagOut = VrefX = VrefH * 199/200
`0xa`	VBG	DiagOut = Vbg from SRSS
`0xe`	I_SOURCE	DiagOut = Isource (10uA)
`0xf`	I_SINK	DiagOut = Isink (10uA)

More details can be found in Technical Reference Manual (TRM), Registers TRM and Data Sheet.

Hardware setup

This CE has been developed for:

TRAVEO™ T2G evaluation kit (KIT_T2G-B-H_EVK)

The VrefH is connected to VDDA in the kit. VDDA is set to 5V. Ensure jumper J10 is in the 5V position (or position 1). VrefL is equal to 0V.
TRAVEO™ T2G Body High Lite evaluation kit (KIT_T2G-B-H_LITE)

The VrefH is connected to VDDA in the kit. VDDA is set to 5V. Ensure jumper J20 and J21 are in the 5V position (or position 3). VrefL is equal to 0V.

A UART serial connection should be made with the computer via the serial port (KitProg3 connector). Use a terminal emulator to see the output on the screen. In the terminal emulator settings, select the KitProg3 COM port and set the baud rate to 115200.

Implementation

In this design, the diagnostic reference component of the ADC module is enabled and configured to supply input voltage to the ADC module. A list of available voltages that can be set as a diagnostic reference is displayed on the terminal program. The user will be able to choose one of the options by entering the character associated with the required reference voltage. The corresponding voltage is set as the diagnostic reference voltage by writing the PASSx_SARy_DIAG_CTL.DIAG_SEL field with the appropriate value.

In the user defined function Process_ADC() the ADC takes this voltage as the input and the output count is then converted into the equivalent analog voltage. If the measured voltage closely aligns with the input voltage within an acceptable margin of error, it instills confidence in the correct operation of the ADC.

STDOUT/STDIN setting

Initialization of the GPIO for UART is done in the cy_retarget_io_init() function.

Initializes the pin specified by CYBSP_DEBUG_UART_TX as UART TX and the pin specified by CYBSP_DEBUG_UART_RX as UART RX (these pins are connected to KitProg3 COM port)
The serial port parameters are 8N1 and 115200 baud

Clock configuration

The CLK_HF2 is a high-frequency clock that can be sourced by IMO, EXT_CLK or ECO. This clock is divided with PeriClk dividers to generate a clock frequency of 3.92 MHz as the input clock to the ADC module. These steps are done by calling PDL functions at cybsp_init().

A sampling time interval of ~30uS is generated using the following calculation,

Sample time = SAMPLE_TIME / SAR clock frequency = 120/(3.92MHz) = 30.61 uS

Where,

SAMPLE_TIME = Sample time in ADC clock cycles. Number which is divided by ADC clock frequency to generate a sampling interval of ~30uS.

SAR ADC initialization

SAR ADC channel 0 is configured and enabled by calling Cy_SAR2_Init() with appropriate arguments using macros and configuration structure cy_stc_sar2_config_t configured by Device Configurator:

Enable diagnostic reference

The diagnostic reference feature is enabled for ADC Channel 0 by using the PDL driver API Cy_SAR2_Diag_Enable() with appropriate arguments. If diagnostic reference is enabled then EPASS_MMIO.PASS_CTL.REFBUF_EN field must be set. This is done using Cy_SAR2_GetReferenceBufferMode().

User input

Using UART serial communication, a list of available reference voltages is displayed on the terminal emulator. The user can enter the corresponding key to choose a value to set the corresponding voltage as the diagnostic reference.

Code Example main loop

The endless loop of the Code Example in main() always checks whether a character has been received from the user via UART (terminal) using cyhal_uart_getc(). The user interface supports numeric values ranging from 0 - 9 and alphabets from a - e (or A - E).

The character received is then written to the PASSx_SARy_DIAG_CTL.DIAG_SEL field using the PDL driver API Cy_SAR2_Diag_Init() with the ADC Channel 0 macro and the diagnostic configuration structure cy_stc_sar2_diag_config_t as arguments. The ADC input reference voltage is now set.

A/D conversion

In the user-defined method Process_ADC(), the PDL driver API Cy_SAR2_Channel_SoftwareTrigger() issues a software trigger to start the A/D conversion. When the conversion is complete, the PDL driver API Cy_SAR2_Channel_GetInterruptStatus() returns the status CY_SAR2_INT_GRP_DONE . The output count resultAN0 is obtained using the PDL driver API Cy_SAR2_Channel_GetResult() , which is then converted to the equivalent analog voltage value using the following formula,

resultMillivolts = MAX_MILLI_VOLTS * (resultAN0/RESULT_MAX);

where,

MAX_MILLI_VOLTS = 5000

RESULT_MAX = 4950

resultAN0 = ADC output counts

The ADC functional correctness can be verified by comparing the output resultMillivolts and the reference voltage set by the user.

Run and Test

For this example, a terminal emulator is required for displaying outputs and to change settings during runtime. Install a terminal emulator if you do not have one. Instructions in this document use Tera Term.

After code compilation, perform the following steps for flashing the device:

Connect the board to your PC using the provided USB cable through the KitProg3 USB connector. Ensure jumper settings are in 5V position.
Open a terminal program and select the KitProg3 COM port. Set the serial port parameters to 8N1 and 115200 baud.
Program the board using one of the following:
- Select the code example project in the Project Explorer.
- In the Quick Panel, scroll down, and click [Project Name] Program (KitProg3_MiniProg4).
After programming, the code example starts automatically. Confirm that the messages are displayed on the UART terminal:

Terminal output on program startup

A list of available reference voltages is displayed. The user can select an option by entering the corresponding character to see the number of counts and the calculated analog voltage value.
You can debug the example to step through the code. In the IDE, use the [Project Name] Debug (KitProg3_MiniProg4) configuration in the Quick Panel. For details, see the "Program and debug" section in the Eclipse IDE for ModusToolbox™ software user guide.

Note: (Only while debugging) On the CM7 CPU, some code in main() may execute before the debugger halts at the beginning of main(). This means that some code executes twice: once before the debugger stops execution, and again after the debugger resets the program counter to the beginning of main(). See KBA231071 to learn about this and for the workaround.