Nuts and Volts - October 2015

bps. The escape character is 0x26, which is issued by a keyboard as Cntl+z and it takes three escape characters to drop into command mode from logging mode. My modification to the CONFIG.TXT file contents is represented by the 2, which tells the OpenLog firmware to come up in command mode instead of logging mode.

Since we want to manipulate the microSD card from a PC using the onboard FTDI USB portal, I left the verbose and echo settings at their defaults. I’ve already done all of the necessary preliminary work of defining the I/O pins and activating the necessary PIC32MX575F512H

peripherals. So, let’s fire up the electronics that support the OpenLog and see if the code works.

Manual Mode

While we are operating the OpenLog in manual mode, we will use the Serial Input/Output Monitor application that comes standard with the CCS C Compiler to issue commands and capture the results.

Our OpenLog firmware will come up in command mode. Our PIC32MX575F512H firmware swallows up the initial prompt to make sure the OpenLog hardware is ready to rock. So, the first command I will issue is the

RESET command, which should return a prompt. As you can see in Screenshot 1, we’ve had a good start. Everything sent and received from the OpenLog is visible in ASCII and hexadecimal form. Once I received a prompt, I entered a character to reveal the available commands. The goal of having this view is to note the characters that surround the data. When we go “microcontroller automatic,” we will need to filter out the characters that are not part of the data we wish to retrieve. For example, note the carriage return/line feed characters before the 0x3E prompt in Secreenshot 2. Keep that in mind as you examine the code we’re about to write.

Initializing the microSD Hardware

The OpenLog was originally designed to be an Arduino accessory. In our case, the OpenLog hardware is under the control of a PIC32MX575F512H, which has access to the ATmega’s RESET pin. Before attempting to issue commands via firmware, the PIC32MX575F512H needs to know if the OpenLog hardware is functional and if a functional microSD card is mounted in the OpenLog’s socket. There is one sure fire way to get the ATmega’s attention

70 October 2015

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■ Screenshot 1. Things are good. The OpenLog firmware is communicating with the Serial Input/Output Monitor application running on my Lenovo laptop by way of the PIC32MX575F512H.