diff --git a/src/mame/chess/regence.cpp b/src/mame/chess/regence.cpp
index 065d4558bf8..7b853de0ac2 100644
--- a/src/mame/chess/regence.cpp
+++ b/src/mame/chess/regence.cpp
@@ -16,8 +16,11 @@ Hardware notes:
 - 2KB battery-backed RAM (MSM5128-15RS), 3 sockets, only middle one used
 - TTL, piezo, 8*8+4 LEDs, magnetic sensors
 
-The hardware triggers an NMI on power-off (or power-failure). If this isn't done,
-NVRAM fails at next power-on.
+NOTE: The hardware triggers an NMI on power-off (or power-failure). If this isn't
+done, NVRAM fails at next power-on.
+
+TODO:
+- if/when MAME supports an exit callback, hook up power-off NMI to that
 
 *******************************************************************************/
 
@@ -49,7 +52,7 @@ public:
 		m_inputs(*this, "IN.%u", 0)
 	{ }
 
-	DECLARE_INPUT_CHANGED_MEMBER(power) { if (newval && m_power) power_off(); }
+	DECLARE_INPUT_CHANGED_MEMBER(power_off);
 
 	// machine configs
 	void regence(machine_config &config);
@@ -75,9 +78,7 @@ private:
 	void leds_w(u8 data);
 	u8 input_r();
 
-	void power_off();
 	bool m_power = false;
-
 	u8 m_inp_mux = 0;
 	u8 m_led_data = 0;
 };
@@ -90,11 +91,14 @@ void regence_state::machine_start()
 	save_item(NAME(m_led_data));
 }
 
-void regence_state::power_off()
+INPUT_CHANGED_MEMBER(regence_state::power_off)
 {
 	// NMI at power-off (it prepares nvram for next power-on)
-	m_maincpu->pulse_input_line(INPUT_LINE_NMI, attotime::zero);
-	m_power = false;
+	if (newval && m_power)
+	{
+		m_maincpu->pulse_input_line(INPUT_LINE_NMI, attotime::zero);
+		m_power = false;
+	}
 }
 
 
@@ -187,7 +191,7 @@ static INPUT_PORTS_START( regence )
 	PORT_BIT(0x80, IP_ACTIVE_HIGH, IPT_UNUSED)
 
 	PORT_START("POWER") // needs to be triggered for nvram to work
-	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, regence_state, power, 0) PORT_NAME("Power Off")
+	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, regence_state, power_off, 0) PORT_NAME("Power Off")
 INPUT_PORTS_END
 
 
diff --git a/src/mame/novag/const.cpp b/src/mame/novag/const.cpp
index c8a7a476f90..4233abbbe25 100644
--- a/src/mame/novag/const.cpp
+++ b/src/mame/novag/const.cpp
@@ -61,6 +61,7 @@ Super Constellation also has a power-off NMI, but it doesn't do anything other
 than writing 0x08 to control_w.
 
 TODO:
+- if/when MAME supports an exit callback, hook up power-off NMI to that
 - is Dynamic S a program update of ssensor4 or identical?
 
 *******************************************************************************/
@@ -102,7 +103,7 @@ public:
 		m_inputs(*this, "IN.%u", 0)
 	{ }
 
-	DECLARE_INPUT_CHANGED_MEMBER(power) { if (newval && m_power) power_off(); }
+	DECLARE_INPUT_CHANGED_MEMBER(power_off);
 
 	// machine configs
 	void nconst(machine_config &config);
@@ -138,9 +139,7 @@ private:
 	u8 input1_r();
 	u8 input2_r();
 
-	void power_off();
 	bool m_power = false;
-
 	u8 m_inp_mux = 0;
 	u8 m_led_select = 0;
 };
@@ -153,11 +152,14 @@ void const_state::machine_start()
 	save_item(NAME(m_led_select));
 }
 
-void const_state::power_off()
+INPUT_CHANGED_MEMBER(const_state::power_off)
 {
 	// NMI at power-off (ssensor4 prepares nvram for next power-on)
-	m_maincpu->pulse_input_line(INPUT_LINE_NMI, attotime::zero);
-	m_power = false;
+	if (newval && m_power)
+	{
+		m_maincpu->pulse_input_line(INPUT_LINE_NMI, attotime::zero);
+		m_power = false;
+	}
 }
 
 void const_state::init_const()
@@ -320,7 +322,7 @@ static INPUT_PORTS_START( ssensor4 )
 	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_KEYPAD) PORT_CODE(KEYCODE_W) PORT_NAME("Hint")
 
 	PORT_START("POWER") // needs to be triggered for nvram to work
-	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, const_state, power, 0) PORT_NAME("Power Off")
+	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, const_state, power_off, 0) PORT_NAME("Power Off")
 INPUT_PORTS_END
 
 static INPUT_PORTS_START( nconstq )
@@ -345,7 +347,7 @@ static INPUT_PORTS_START( sconst )
 	PORT_BIT(0x02, IP_ACTIVE_HIGH, IPT_KEYPAD) PORT_CODE(KEYCODE_3) PORT_NAME("Print List / Acc. Time / Pawn")
 
 	PORT_START("POWER")
-	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, const_state, power, 0) PORT_NAME("Power Off")
+	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, const_state, power_off, 0) PORT_NAME("Power Off")
 INPUT_PORTS_END
 
 
diff --git a/src/mame/novag/snova.cpp b/src/mame/novag/snova.cpp
index 2e1c3d46d45..872429076f8 100644
--- a/src/mame/novag/snova.cpp
+++ b/src/mame/novag/snova.cpp
@@ -6,9 +6,11 @@
 Novag Super Nova & related chess computers. I believe the series started with
 Primo. The chess engine is by David Kittinger.
 
+NOTE: nsnova does an NMI at power-off (or power-failure). If this isn't done,
+NVRAM won't work properly (supremo doesn't have NVRAM).
+
 TODO:
-- NMI on power-off switch, it sets 0x14 bit 7 for standby power (see below)
-- add nvram, MCU is missing standby power emulation
+- if/when MAME supports an exit callback, hook up power-off NMI to that
 - beeps are glitchy, as if interrupted for too long
 - nsnova serial port isn't working, MCU emulation problem?
 - nsnova unmapped reads from 0x33/0x34
@@ -50,6 +52,7 @@ The model number is still 881, ROM is the same as the standard fake-wood version
 
 #include "bus/rs232/rs232.h"
 #include "cpu/m6800/m6801.h"
+#include "machine/nvram.h"
 #include "machine/sensorboard.h"
 #include "sound/dac.h"
 #include "video/pwm.h"
@@ -79,6 +82,8 @@ public:
 		m_out_lcd(*this, "s%u.%u", 0U, 0U)
 	{ }
 
+	DECLARE_INPUT_CHANGED_MEMBER(power_off);
+
 	// machine configs
 	void snova(machine_config &config);
 	void supremo(machine_config &config);
@@ -100,6 +105,7 @@ private:
 	void snova_map(address_map &map);
 	void supremo_map(address_map &map);
 
+	void standby(int state);
 	void lcd_pwm_w(offs_t offset, u8 data);
 	void update_leds();
 
@@ -131,6 +137,26 @@ void snova_state::machine_start()
     I/O
 *******************************************************************************/
 
+// power
+
+void snova_state::standby(int state)
+{
+	// clear display
+	if (state)
+	{
+		m_lcd_pwm->clear();
+		m_led_pwm->clear();
+	}
+}
+
+INPUT_CHANGED_MEMBER(snova_state::power_off)
+{
+	// NMI at power-off, which will trigger standby mode
+	if (newval && !m_maincpu->standby())
+		m_maincpu->pulse_input_line(INPUT_LINE_NMI, attotime::zero);
+}
+
+
 // misc
 
 void snova_state::lcd_pwm_w(offs_t offset, u8 data)
@@ -223,7 +249,8 @@ void snova_state::supremo_map(address_map &map)
 void snova_state::snova_map(address_map &map)
 {
 	supremo_map(map);
-	map(0x4000, 0x5fff).ram();
+	map(0x0040, 0x013f).ram().share("internal"); // internal
+	map(0x4000, 0x5fff).ram().share("nvram");
 }
 
 
@@ -252,6 +279,9 @@ static INPUT_PORTS_START( snova )
 	PORT_BIT(0x20, IP_ACTIVE_HIGH, IPT_KEYPAD) PORT_CODE(KEYCODE_E) PORT_NAME("Set Up / Verify")
 	PORT_BIT(0x40, IP_ACTIVE_HIGH, IPT_KEYPAD) PORT_CODE(KEYCODE_W) PORT_NAME("Random / Auto Clock")
 	PORT_BIT(0x80, IP_ACTIVE_HIGH, IPT_KEYPAD) PORT_CODE(KEYCODE_Q) PORT_NAME("New Game")
+
+	PORT_START("POWER") // needs to be triggered for nvram to work
+	PORT_BIT(0x01, IP_ACTIVE_HIGH, IPT_OTHER) PORT_CODE(KEYCODE_F1) PORT_CHANGED_MEMBER(DEVICE_SELF, snova_state, power_off, 0) PORT_NAME("Power Off")
 INPUT_PORTS_END
 
 static INPUT_PORTS_START( supremo )
@@ -282,11 +312,11 @@ INPUT_PORTS_END
     Machine Configs
 *******************************************************************************/
 
-void snova_state::snova(machine_config &config)
+void snova_state::supremo(machine_config &config)
 {
 	// basic machine hardware
-	HD6303Y(config, m_maincpu, 16_MHz_XTAL);
-	m_maincpu->set_addrmap(AS_PROGRAM, &snova_state::snova_map);
+	HD6303Y(config, m_maincpu, 8_MHz_XTAL);
+	m_maincpu->set_addrmap(AS_PROGRAM, &snova_state::supremo_map);
 	m_maincpu->in_p2_cb().set(FUNC(snova_state::p2_r));
 	m_maincpu->out_p2_cb().set(FUNC(snova_state::p2_w));
 	m_maincpu->out_p5_cb().set(FUNC(snova_state::p5_w));
@@ -306,29 +336,33 @@ void snova_state::snova(machine_config &config)
 	screen.set_visarea_full();
 
 	PWM_DISPLAY(config, m_led_pwm).set_size(2, 8);
-	config.set_default_layout(layout_novag_snova);
+	config.set_default_layout(layout_novag_supremo);
 
 	// sound hardware
 	SPEAKER(config, "speaker").front_center();
 	DAC_1BIT(config, m_dac).add_route(ALL_OUTPUTS, "speaker", 0.25);
+}
+
+void snova_state::snova(machine_config &config)
+{
+	supremo(config);
+
+	// basic machine hardware
+	m_maincpu->set_clock(16_MHz_XTAL);
+	m_maincpu->set_addrmap(AS_PROGRAM, &snova_state::snova_map);
+	m_maincpu->nvram_enable_backup(true);
+	m_maincpu->standby_cb().set(FUNC(snova_state::standby));
+
+	NVRAM(config, "internal", nvram_device::DEFAULT_ALL_0);
+	NVRAM(config, "nvram", nvram_device::DEFAULT_ALL_0);
+	m_board->set_nvram_enable(true);
+
+	config.set_default_layout(layout_novag_snova);
 
 	// rs232 (configure after video)
 	RS232_PORT(config, m_rs232, default_rs232_devices, nullptr);
 }
 
-void snova_state::supremo(machine_config &config)
-{
-	snova(config);
-
-	// basic machine hardware
-	m_maincpu->set_clock(8_MHz_XTAL);
-	m_maincpu->set_addrmap(AS_PROGRAM, &snova_state::supremo_map);
-
-	config.set_default_layout(layout_novag_supremo);
-
-	config.device_remove("rs232");
-}
-
 
 
 /*******************************************************************************
diff --git a/src/mame/saitek/leonardo.cpp b/src/mame/saitek/leonardo.cpp
index 0a42d0c6fa7..3b5acd59c71 100644
--- a/src/mame/saitek/leonardo.cpp
+++ b/src/mame/saitek/leonardo.cpp
@@ -14,10 +14,10 @@ The expansion modules are basically entire chesscomputers, making the whole
 thing combined a 'dual brain' chesscomputer. The embedded chess engine is by
 Julio Kaplan and Craig Barnes, same as the one in SciSys Turbo S-24K.
 
-NOTE: In order for nvram to work properly, press the STOP button to turn off
+NOTE: In order for NVRAM to work properly, press the STOP button to turn off
 the chesscomputer before exiting MAME. Other than ACL (which is an unemulated
 hardware button that disconnects the battery), there is no known method to
-force a cold boot. So if nvram somehow becomes broken, remove the nvram files.
+force a cold boot. So if NVRAM somehow becomes broken, remove the NVRAM files.
 
 Hardware notes:
 
@@ -55,7 +55,7 @@ to be upgraded with an EMI PCB (power supply related, meaningless for emulation)
 
 TODO:
 - OSA PC link, uses MCU serial interface
-- MCU internal nvram belongs in m6801.cpp
+- MCU internal NVRAM belongs in m6801.cpp
 
 *******************************************************************************/
 
diff --git a/src/mame/saitek/renaissance.cpp b/src/mame/saitek/renaissance.cpp
index e356fd25b41..ede99f36b7c 100644
--- a/src/mame/saitek/renaissance.cpp
+++ b/src/mame/saitek/renaissance.cpp
@@ -8,7 +8,7 @@ Saitek Kasparov Renaissance
 Saitek's 2nd version modular chesscomputer. It accepts the same modules as
 Leonardo/Galileo. "OSA" version for Renaissance is 1.5.
 
-NOTE: In order for nvram to work properly, press the STOP button to turn off
+NOTE: In order for NVRAM to work properly, press the STOP button to turn off
 the chesscomputer before exiting MAME. Unlike Leonardo/Galileo, it looks like
 it will always do a cold boot if you reset without having pressed STOP.