diff --git a/CMakeLists.txt b/CMakeLists.txt
index ad215c2..32b5926 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,6 +15,7 @@ add_executable(
   cpu.cpp
   debugger.cpp
   error.cpp
+  kw11-l.cpp
   main.cpp
   memory.cpp
   rk05.cpp
diff --git a/bus.cpp b/bus.cpp
index 06e8570..e08e8c8 100644
--- a/bus.cpp
+++ b/bus.cpp
@@ -80,8 +80,7 @@ uint16_t bus::read(const uint16_t a, const bool word_mode, const bool use_prev,
 
 		if (a == 0177546) { // line frequency clock and status register
 			D(fprintf(stderr, "read line freq clock\n");)
-			CSR |= 128;
-			return CSR;
+			return lf_csr;
 		}
 
 		if (a == 0177514) { // printer, CSR register, LP11
@@ -533,8 +532,8 @@ uint16_t bus::write(const uint16_t a, const bool word_mode, uint16_t value, cons
 
 		if (a == 0177546) { // line frequency clock and status register
 			D(fprintf(stderr, "write set LFC/SR: %o\n", value);)
-			CSR = value;
-			return CSR;
+			lf_csr = value;
+			return lf_csr;
 		}
 
 		if (tm11 && a >= TM_11_BASE && a < TM_11_END) {
@@ -721,3 +720,13 @@ void bus::writeUnibusByte(const uint16_t a, const uint8_t v)
 {
 	m->writeByte(a, v);
 }
+
+void bus::set_lf_crs_b7()
+{
+	lf_csr |= 128;
+}
+
+uint8_t bus::get_lf_crs()
+{
+	return lf_csr;
+}
diff --git a/bus.h b/bus.h
index ad593f7..0ce7138 100644
--- a/bus.h
+++ b/bus.h
@@ -36,6 +36,8 @@ private:
 
 	uint16_t switch_register { 0 };
 
+	uint16_t lf_csr { 0 };
+
 	bool     debug_mode { false };
 
 public:
@@ -58,6 +60,9 @@ public:
 
 	void init();  // invoked by 'RESET' command
 
+	void    set_lf_crs_b7();
+	uint8_t get_lf_crs();
+
 	uint16_t read(const uint16_t a, const bool word_mode, const bool use_prev, const bool peek_only=false);
 	uint16_t readByte(const uint16_t a) { return read(a, true, false); }
 	uint16_t readWord(const uint16_t a);
diff --git a/cpu.cpp b/cpu.cpp
index d58f2fd..d520a34 100644
--- a/cpu.cpp
+++ b/cpu.cpp
@@ -247,6 +247,8 @@ void cpu::setPSW(const uint16_t v, const bool limited)
 
 bool cpu::check_queued_interrupts()
 {
+	std::unique_lock<std::mutex> lck(qi_lock);
+
 	uint8_t current_level = getPSW_spl();
 
 	// uint8_t start_level = current_level <= 3 ? 0 : current_level + 1;
@@ -273,6 +275,8 @@ bool cpu::check_queued_interrupts()
 
 void cpu::queue_interrupt(const uint8_t level, const uint8_t vector)
 {
+	std::unique_lock<std::mutex> lck(qi_lock);
+
 	auto it = queued_interrupts.find(level);
 
 	it->second.insert(vector);
diff --git a/cpu.h b/cpu.h
index ecb2f77..0d27c11 100644
--- a/cpu.h
+++ b/cpu.h
@@ -4,6 +4,7 @@
 
 #include <assert.h>
 #include <map>
+#include <mutex>
 #include <set>
 #include <stdint.h>
 #include <vector>
@@ -27,6 +28,7 @@ private:
 
 	// level, vector
 	std::map<uint8_t, std::set<uint8_t> > queued_interrupts;
+	std::mutex qi_lock;
 
 	std::set<uint16_t> breakpoints;
 
diff --git a/kw11-l.cpp b/kw11-l.cpp
new file mode 100644
index 0000000..18637b6
--- /dev/null
+++ b/kw11-l.cpp
@@ -0,0 +1,31 @@
+#include <unistd.h>
+
+#include "cpu.h"
+#include "kw11-l.h"
+
+
+kw11_l::kw11_l(bus *const b) : b(b)
+{
+	th = new std::thread(std::ref(*this));
+}
+
+kw11_l::~kw11_l()
+{
+	stop_flag = true;
+
+	th->join();
+
+	delete th;
+}
+
+void kw11_l::operator()()
+{
+	while(!stop_flag) {
+		b->set_lf_crs_b7();
+
+		if (b->get_lf_crs() & 64)
+			b->getCpu()->queue_interrupt(6, 0100);
+
+		usleep(1000000 / 50);
+	}
+}
diff --git a/kw11-l.h b/kw11-l.h
new file mode 100644
index 0000000..88158db
--- /dev/null
+++ b/kw11-l.h
@@ -0,0 +1,19 @@
+#include <atomic>
+#include <thread>
+
+#include "bus.h"
+
+
+class kw11_l
+{
+private:
+	bus         *const b         { nullptr };
+	std::thread *      th        { nullptr };
+	std::atomic_bool   stop_flag { false };
+
+public:
+	kw11_l(bus *const b);
+	virtual ~kw11_l();
+
+	void operator()();
+};
diff --git a/main.cpp b/main.cpp
index c3fc893..4a4ff9f 100644
--- a/main.cpp
+++ b/main.cpp
@@ -13,6 +13,7 @@
 #include "cpu.h"
 #include "debugger.h"
 #include "gen.h"
+#include "kw11-l.h"
 #include "memory.h"
 #include "terminal.h"
 #include "tests.h"
@@ -160,9 +161,12 @@ int main(int argc, char *argv[])
 	//setlocale(LC_ALL, "");
 
 	bus *b = new bus();
+
 	cpu *c = new cpu(b, &event);
 	b->add_cpu(c);
 
+	kw11_l *lf = new kw11_l(b);
+
 	c -> setEmulateMFPT(true);
 
 	std::vector<std::string> rk05_files;