Adding arduino micro sd card example

Adding Arduino micro SD card example for the Grand Central M4

Grand_Central_M4_Arduino_SD_Card/Grand_Central_M4_Arduino_SD_Card.ino

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+// SPDX-FileCopyrightText: 2023 Liz Clark for Adafruit Industries
+//
+// SPDX-License-Identifier: MIT
+/*
+  SD card read/write
+
+ This example shows how to read and write data to and from an SD card file
+ The circuit:
+ * SD card attached to SPI bus as follows:
+ ** MOSI - pin 64
+ ** MISO - pin 66
+ ** CLK - pin 65
+
+ created   Nov 2010
+ by David A. Mellis
+ modified 9 Apr 2012
+ by Tom Igoe
+ modified 14 Feb 2023
+ by Liz Clark
+
+ This example code is in the public domain.
+
+ */
+
+#include <SPI.h>
+//#include <SD.h>
+#include "SdFat.h"
+SdFat SD;
+
+#define SD_FAT_TYPE 3
+
+// default CS pin is SDCARD_SS_PIN (83) for Grand Central M4
+#define SD_CS_PIN SDCARD_SS_PIN
+
+File myFile;
+
+void setup() {
+  // Open serial communications and wait for port to open:
+  Serial.begin(115200);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for native USB port only
+  }
+
+
+  Serial.print("Initializing SD card...");
+
+  if (!SD.begin(SD_CS_PIN)) {
+    Serial.println("initialization failed!");
+    return;
+  }
+  Serial.println("initialization done.");
+
+  // open the file. note that only one file can be open at a time,
+  // so you have to close this one before opening another.
+  myFile = SD.open("test.txt", FILE_WRITE);
+
+  // if the file opened okay, write to it:
+  if (myFile) {
+    Serial.print("Writing to test.txt...");
+    myFile.println("testing 1, 2, 3.");
+    myFile.println("hello grand central m4!");
+    // close the file:
+    myFile.close();
+    Serial.println("done.");
+  } else {
+    // if the file didn't open, print an error:
+    Serial.println("error opening test.txt");
+  }
+
+  // re-open the file for reading:
+  myFile = SD.open("test.txt");
+  if (myFile) {
+    Serial.println("test.txt:");
+
+    // read from the file until there's nothing else in it:
+    while (myFile.available()) {
+      Serial.write(myFile.read());
+    }
+    // close the file:
+    myFile.close();
+  } else {
+    // if the file didn't open, print an error:
+    Serial.println("error opening test.txt");
+  }
+}
+
+void loop() {
+  // nothing happens after setup
+}