diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme
index 2cfe830df..6609a35c0 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme	
@@ -68,7 +68,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Release"
+      buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
diff --git a/Storage/Tape/Formats/ZX80O.cpp b/Storage/Tape/Formats/ZX80O.cpp
index 74407dd00..161651c5e 100644
--- a/Storage/Tape/Formats/ZX80O.cpp
+++ b/Storage/Tape/Formats/ZX80O.cpp
@@ -13,20 +13,88 @@ using namespace Storage::Tape;
 ZX80O::ZX80O(const char *file_name) :
 	Storage::FileHolder(file_name) {
 
+	// Files can be no longer than 16 kb
+	if(file_stats_.st_size > 16384) throw ErrorNotZX80O;
+
+	// skip the system area
+	fseek(file_, 8, SEEK_SET);
+
+	// read the pointer to VARS and the alleged pointer to end of file
+	uint16_t vars = fgetc16le();
+	end_of_file_ = fgetc16le();
+
+	// VARs should be before end of file
+	if(vars > end_of_file_) throw ErrorNotZX80O;
+
+	// end of file should be no further than the actual file size
+	if(end_of_file_ - 0x4000 > file_stats_.st_size) throw ErrorNotZX80O;
+
+	// TODO: does it make sense to inspect the tokenised BASIC?
+	// It starts at 0x4028 and proceeds as [16-bit line number] [tokens] [0x76],
+	// but I'm as yet unable to find documentation of the tokens.
+
 	// then rewind and start again
 	virtual_reset();
 }
 
 void ZX80O::virtual_reset() {
 	fseek(file_, 0, SEEK_SET);
+	is_past_silence_ = false;
+	is_high_ = true;
+	bit_pointer_ = 9;
 }
 
 bool ZX80O::is_at_end() {
-	return feof(file_);
+	return ftell(file_) == end_of_file_ - 0x4000;
 }
 
 Tape::Pulse ZX80O::virtual_get_next_pulse() {
 	Tape::Pulse pulse;
 
+	// Start with 1 second of silence.
+	if(!is_past_silence_) {
+		pulse.type = Pulse::Type::Zero;
+		pulse.length.length = 1;
+		pulse.length.clock_rate = 1;
+		is_past_silence_ = true;
+		return pulse;
+	}
+
+	// For each byte, output 8 bits and then silence.
+	if(bit_pointer_ == 9) {
+		byte_ = (uint8_t)fgetc(file_);
+		bit_pointer_ = 0;
+		wave_pointer_ = 0;
+	}
+
+	// Bytes are stored MSB first.
+	if(bit_pointer_ < 8) {
+		// waves are of length 150µs
+		pulse.length.length = 3;
+		pulse.length.clock_rate = 20000;
+
+		if(is_high_) {
+			pulse.type = Pulse::Type::High;
+			is_high_ = false;
+		} else {
+			pulse.type = Pulse::Type::Low;
+			is_high_ = true;
+
+			int wave_count = (byte_ & (0x80 >> bit_pointer_)) ? 9 : 4;
+			wave_pointer_++;
+			if(wave_pointer_ == wave_count) {
+				bit_pointer_++;
+				wave_pointer_ = 0;
+			}
+		}
+	} else {
+		// post-waves silence is 1300µs
+		pulse.length.length = 13;
+		pulse.length.clock_rate = 10000;
+		pulse.type = Pulse::Type::Zero;
+
+		bit_pointer_++;
+	}
+
 	return pulse;
 }
diff --git a/Storage/Tape/Formats/ZX80O.hpp b/Storage/Tape/Formats/ZX80O.hpp
index e486c0b96..5535adea5 100644
--- a/Storage/Tape/Formats/ZX80O.hpp
+++ b/Storage/Tape/Formats/ZX80O.hpp
@@ -38,6 +38,14 @@ class ZX80O: public Tape, public Storage::FileHolder {
 	private:
 		void virtual_reset();
 		Pulse virtual_get_next_pulse();
+
+		uint8_t byte_;
+		int bit_pointer_;
+		int wave_pointer_;
+		bool is_past_silence_;
+		bool is_high_;
+
+		uint16_t end_of_file_;
 };
 
 }