Leveraging High Resolution Capture (HRCAP) for Single Wire Data Transfer

In various industrial and automotive applications, it is often required to transfer data between two electrically isolated devices. The standard protocols require more than one communication line to transfer data, which leads to the use of multiple isolation buffers that ultimately increase the system cost. Also, in case of standard serial protocols, unit pulse/clock is used to encode only a single bit. This application report discusses how to leverage the high resolution capture unit in C2000™ to improve the transmission latency and reduce the cost by facilitating data transfer in just a single pulse through a single wire. The experimental setup details and results are also being discussed in this application report. You can quickly verify and utilize this system in various applications using the provided algorithm and source code that can be downloaded from the C2000Ware.

Trademarks

C2000 is a registered trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

1 Introduction

Pulse Width Modulation (PWM) is a powerful way of encoding analog signal levels and is commonly used for controlling DC power to an electrical device. PWM can also be used for data transmission by varying the output pulse width proportionally with the data to be transferred, but a powerful decoding unit is required at the receiver. Normal capture peripheral eCAP cannot support high transmission frequencies for high resolution data communication, which results in a high latency solution. However, HRCAP of C2000 operates over and above standard eCAP and is capable of measuring width of external pulses to a higher degree of accuracy compared to standard capture unit eCAP. Thus, using HRCAP as a decoding unit at the receiver adds differentiation to the system by significantly reducing the latency for high resolution data transfer.

The application report describes the high resolution peripherals of C2000 in brief and discusses the system implementation details. The document also discusses the software flow of both the transmitter and receiver examples and the achieved effective number of bits (ENOB) and latency at various transmission frequencies. Use Table 1 to choose various parameters while designing your own system. The showcasing example configures F2838x as transmitter and F28004x as receiver, but the software can easily be ported to any C2000 device that supports HRCAP Type 1. Also in order to quickly evaluate the system, the single device loopback example is also provided where the same F28004x device is used as both transmitter and receiver.

The showcasing example code discussed in this document can be found in C2000Ware v2.00.00.03 or latest, located within the following local directory after installation:

C:\ti\c2000\C2000Ware_<version_number>\demo_examples\hrcap_hrpwm_data_transfer

The available example projects are:

cross_device_data_tansfer\Transmitter
cross_device_data_tansfer\Receiver
device_loopback

2 System Showcase

The showcasing data communication system utilizes the high resolution PWM (HRPWM) module of C2000 as an encoding unit and high resolution capture (HRCAP) of C2000 as decoding unit. Figure 1 illustrates the transmitter and the receiver blocks. Based on the analog input sampled by transmitter, CPU configures the high resolution PWM signal that is then captured using high resolution capture at receiver and the decoded data is communicated to CPU.

Figure 1. Transmitter and Receiver Blocks