SPI not working with MBED (was: Performance of XIAO with Sharp Memory Display)

#include <SPI.h>

// define Xiao CS
#define CS 7

SPISettings settings(1000000, MSBFIRST, SPI_MODE0);

void setup() {

Serial.begin(9600);

SPI.begin();

pinMode(CS,OUTPUT);
digitalWrite(CS, HIGH);

}

void loop() {

SPI.beginTransaction(settings);
digitalWrite(CS, LOW);
SPI.transfer(0x00); // Address to read from peripheral
SPI.transfer(0x80); // Byte signalling read instruction to peripheral
uint8_t readByte = SPI.transfer(0xFF); // Sent DONT CARE byte and receive peripheral data
digitalWrite(CS, HIGH);

Serial.print(“0x”);
Serial.println(readByte, HEX);
delay(10);
SPI.endTransaction();

delay(1000);

}