There are a few changes I made to the standard RunCPM.  It is easier for me to describe them than fork a copy of Marcelo's code.

Since the Power LED connected to Pin 12, I added the following define:

#define POWLED 12

In setup() I added the following to light the Power LED:

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

I also set the serial speed to 115,200:

 Serial.begin(115200);

I altered loop() so the LEDs blink alternately after CP/M exits:

void loop(void) {
 digitalWrite(POWLED, HIGH);
 delay(500);
 digitalWrite(POWLED, LOW);
 delay(1000);
 digitalWrite(LED, HIGH);
 delay(500);
 digitalWrite(LED, LOW);
 delay(1000);
}