diff --git a/src/zap/zap.h b/src/zap/zap.h
index e3d26bb..5e5ab97 100644
--- a/src/zap/zap.h
+++ b/src/zap/zap.h
@@ -25,9 +25,10 @@ static inline void zap_init(enum zap_component zc) {
 	if (zc & zap_crowbar) zap_crowbar_init();
 	if (zc & zap_dac) zap_dac_init();
 	if (zc & zap_gpio) zap_gpio_init(false, true);
-	if (zc & zap_max4619) zap_max_init(false);
+	if (zc & zap_max4619) zap_max_init(false, false);
 	if (zc & zap_picoemp) zap_picoemp_init();
 }
+// TODO: deinit stuff (also in submodules)
 
 static inline void zap_init_default(void) {
 	zap_init(zap_adc | zap_crowbar | zap_dac | zap_gpio | zap_max4619);
diff --git a/src/zap/zap_max4619.c b/src/zap/zap_max4619.c
index c5d7a7f..41a327f 100644
--- a/src/zap/zap_max4619.c
+++ b/src/zap/zap_max4619.c
@@ -8,7 +8,7 @@
 
 #include "zap_max4619.h"
 
-void zap_max_init(bool inhibit) {
+void zap_max_init(bool inhibit, bool use_jp300) {
 	const io_rw_32 pinmask = 1u << ZAP_GLITCH_OUT;
 
 	sio_hw->gpio_clr = pinmask; // default to low -> JP300
@@ -18,6 +18,10 @@ void zap_max_init(bool inhibit) {
 	gpio_set_drive_strength(ZAP_GLITCH_OUT, GPIO_DRIVE_STRENGTH_12MA);
 	gpio_set_function(ZAP_GLITCH_OUT, GPIO_FUNC_SIO);
 
+	gpio_put(ZAP_MAX_VHI_SW, use_jp300);
+	gpio_set_dir(ZAP_MAX_VHI_SW, GPIO_OUT);
+	gpio_set_function(ZAP_MAX_VHI_SW, GPIO_FUNC_SIO);
+
 	gpio_put(ZAP_MAX_INHIBIT, inhibit);
 	gpio_set_dir(ZAP_MAX_INHIBIT, GPIO_OUT);
 	gpio_set_function(ZAP_MAX_INHIBIT, GPIO_FUNC_SIO);
diff --git a/src/zap/zap_max4619.h b/src/zap/zap_max4619.h
index dd652f5..3e7b42c 100644
--- a/src/zap/zap_max4619.h
+++ b/src/zap/zap_max4619.h
@@ -8,13 +8,18 @@
 
 #include "zap_pinout.h"
 
-void zap_max_init(bool inhibit);
+void zap_max_init(bool inhibit, bool use_jp300);
 
 static inline void zap_max_set_inhibit(bool inhibit) {
 	if (inhibit) sio_hw->gpio_set = 1u << ZAP_MAX_INHIBIT;
 	else sio_hw->gpio_clr = 1u << ZAP_MAX_INHIBIT;
 }
 
+static inline void zap_max_use_vhi_jp300(bool use_jp300 /* if false: use Vdac1 */) {
+	if (use_jp300) sio_hw->gpio_set = 1u << ZAP_MAX_VHI_SW;
+	else sio_hw->gpio_clr = 1u << ZAP_MAX_VHI_SW;
+}
+
 static inline void zap_max_put(bool low) {
 	if (low) sio_hw->gpio_set = 1u << ZAP_GLITCH_OUT;
 	else sio_hw->gpio_clr = 1u << ZAP_GLITCH_OUT;
diff --git a/src/zap/zap_pinout.h b/src/zap/zap_pinout.h
index 01a4037..f2edf0e 100644
--- a/src/zap/zap_pinout.h
+++ b/src/zap/zap_pinout.h
@@ -12,6 +12,7 @@
 #define ZAP_CROWBAR_2  13
 
 #define ZAP_MAX_INHIBIT 16
+#define ZAP_MAX_VHI_SW  21
 #define ZAP_GPIO_ENABLE 22
 
 #define ZAP_DAC_SPI    spi0