diff --git a/CMakeLists.txt b/CMakeLists.txt
index 29ceafa..2fee93a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,8 +24,8 @@ add_executable(
 include(CheckIPOSupported)
 check_ipo_supported(RESULT supported)
 
-set(CMAKE_BUILD_TYPE RelWithDebInfo)
-#set(CMAKE_BUILD_TYPE Debug)
+#set(CMAKE_BUILD_TYPE RelWithDebInfo)
+set(CMAKE_BUILD_TYPE Debug)
 
 set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
 set(THREADS_PREFER_PTHREAD_FLAG TRUE)
diff --git a/cpu.cpp b/cpu.cpp
index 2415f84..ea6985a 100644
--- a/cpu.cpp
+++ b/cpu.cpp
@@ -139,7 +139,7 @@ void cpu::setPSW_n(const bool v)
 
 void cpu::setPSW_spl(const int v)
 {
-	psw &= 7 << 5;
+	psw &= ~(7 << 5);
 	psw |= v << 5;
 }
 
diff --git a/tests.cpp b/tests.cpp
index 6d0ec3d..16f8d02 100644
--- a/tests.cpp
+++ b/tests.cpp
@@ -69,27 +69,27 @@ void test__registers(cpu *const c)
 
 	// PSW
 	c -> reset();
-	assert(c -> getPSW() == 0);
+	assert(c -> getPSW() == 0 | (7 << 5));
 
 	c -> reset();
         c -> setPSW_c(true);
-	assert(c -> getPSW() == 1);
+	assert(c -> getPSW() == 1 | (7 << 5));
 
 	c -> reset();
 	c -> setPSW_v(true);
-	assert(c -> getPSW() == 2);
+	assert(c -> getPSW() == 2 | (7 << 5));
 
 	c -> reset();
 	c -> setPSW_z(true);
-	assert(c -> getPSW() == 4);
+	assert(c -> getPSW() == 4 | (7 << 5));
 
 	c -> reset();
 	c -> setPSW_n(true);
-	assert(c -> getPSW() == 8);
+	assert(c -> getPSW() == 8 | (7 << 5));
 
 	c -> reset();
-	c -> setPSW_spl(7);
-	assert(c -> getPSW() == (7 << 5));
+	c -> setPSW_spl(1);
+	assert(c -> getPSW() == (1 << 5));
 }
 
 void test_cmp(cpu *const c)
@@ -1391,9 +1391,11 @@ void test_rts(cpu *const c)
 	c -> setRegister(6, 01000);
 	b -> writeWord(0, 0004010);
 	b -> writeWord(10, 0b0000000010000000);
-	do_test(c, 2);
-	assert(c -> getRegister(0) == 10);
+	do_test(c, 1);
 	assert(c -> getRegister(6) == 0776);
+	do_test(c, 1);
+	assert(c -> getRegister(0) == 10);
+	assert(c -> getRegister(6) == 01000);
 	assert(c -> getRegister(7) == 2);
 	//
 	c -> reset();
@@ -1698,7 +1700,7 @@ void test_swab(cpu *const c)
 	b -> writeWord(0, 000301);	// SWAB R1
 	do_test(c, 1);
 	assert(c -> getRegister(1) == 0177577);
-	assert(c -> getPSW_n());
+	assert(!c -> getPSW_n());
 	assert(!c -> getPSW_z());
 	assert(!c -> getPSW_v());
 	assert(!c -> getPSW_c());
diff --git a/tty.cpp b/tty.cpp
index af6a4f3..befd9a6 100644
--- a/tty.cpp
+++ b/tty.cpp
@@ -112,6 +112,8 @@ void tty::writeWord(const uint16_t addr, uint16_t v)
 	if (addr == PDP11TTY_TPB) {
 		char c = v & 127;
 
+		D(fprintf(stderr, "PDP11TTY print '%c'\n", c);)
+
 #if defined(ESP32)
 		if (xQueueSend(queue, &c, portMAX_DELAY) != pdTRUE)
 			Serial.println(F("queue TTY character failed"));