diff --git a/README.md b/README.md
index c3d658f..1cf1d36 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,15 @@
 Apple-1 Emulator
 ================
-
+- Emulates an Apple-1 with 32k of RAM
 - see [napple1](https://github.com/nobuh/napple1)
 - see also [krusader](http://school.anhb.uwa.edu.au/personalpages/kwessen/apple1/Krusader.htm)
+
+Keyboard
+--------
+- F1: reset
+- F2: advance tape
+- F3: rewind tape
+- F4: load program from tape (by simulating typing it)
+- F6: checkpoint machine
+- F7: restore from current checkpoint on tape
+- F8: enter debug mode (display current processor status on serial port)
diff --git a/apple1.ino b/apple1.ino
index 16e1619..902b1e5 100644
--- a/apple1.ino
+++ b/apple1.ino
@@ -34,7 +34,7 @@ void status(const char *fmt, ...) {
 }
 
 jmp_buf ex;
-r6502 cpu(&memory, &ex, status);
+r6502 cpu(memory, &ex, status);
 bool halted = false;
 const char *filename;
 
diff --git a/io.cpp b/io.cpp
index d0d3391..7024558 100644
--- a/io.cpp
+++ b/io.cpp
@@ -145,13 +145,14 @@ void io::write_portb(byte b) {
 
 byte io::read_porta_cr() {
 	byte b = pia::read_porta_cr();
-	if (b == 0xa7) {
-		if (_loading) {
-			if (tape.more())
-				enter(tape.read());
-			else
-				_loading = false;
-		}
+	if (b != 0xa7)
+		return b;
+
+	if (_loading) {
+		if (tape.more())
+			enter(tape.read());
+		else
+			_loading = false;
 	}
 	return b;
 }
diff --git a/pia.cpp b/pia.cpp
index 408867b..9ede66e 100644
--- a/pia.cpp
+++ b/pia.cpp
@@ -3,6 +3,11 @@
 #include "pia.h"
 
 void pia::operator=(byte b) {
+Serial.print(millis());
+Serial.print(" > ");
+Serial.print(_acc, 16);
+Serial.print(' ');
+Serial.println(b, 16);
 	switch(_acc % 4) {
 	case 0:
 		write_porta(b);
@@ -20,6 +25,11 @@ void pia::operator=(byte b) {
 }
 
 pia::operator byte() {
+/*
+Serial.print(millis());
+Serial.print(" < ");
+Serial.println(_acc, 16);
+*/
 	switch (_acc % 4) {
 	case 0:
 		return read_porta();