diff --git a/klippy/pins.py b/klippy/pins.py
index 47bd87b5..90679ad1 100644
--- a/klippy/pins.py
+++ b/klippy/pins.py
@@ -215,8 +215,10 @@ class PrinterPins:
                    share_type=None):
         desc = pin_desc.strip()
         pullup = invert = 0
-        if can_pullup and desc.startswith('^'):
+        if can_pullup and (desc.startswith('^') or desc.startswith('~')):
             pullup = 1
+            if desc.startswith('~'):
+                pullup = -1
             desc = desc[1:].strip()
         if can_invert and desc.startswith('!'):
             invert = 1
@@ -227,7 +229,7 @@ class PrinterPins:
             chip_name, pin = [s.strip() for s in desc.split(':', 1)]
         if chip_name not in self.chips:
             raise error("Unknown pin chip name '%s'" % (chip_name,))
-        if [c for c in '^!: ' if c in pin]:
+        if [c for c in '^~!: ' if c in pin]:
             format = ""
             if can_pullup:
                 format += "[^] "
diff --git a/src/atsam/gpio.c b/src/atsam/gpio.c
index 5308e546..768a3949 100644
--- a/src/atsam/gpio.c
+++ b/src/atsam/gpio.c
@@ -28,6 +28,28 @@ static Pio * const digital_regs[] = {
  * Pin multiplexing
  ****************************************************************/
 
+static void
+set_pull_up(Pio *regs, uint32_t bit, int32_t pull_up)
+{
+#if CONFIG_MACH_SAM3X
+    if (pull_up > 0)
+        regs->PIO_PUER = bit;
+    else
+        regs->PIO_PUDR = bit;
+#else
+    if (pull_up > 0) {
+        regs->PIO_PPDDR = bit;
+        regs->PIO_PUER = bit;
+    } else if (pull_up < 0) {
+        regs->PIO_PUDR = bit;
+        regs->PIO_PPDER = bit;
+    } else {
+        regs->PIO_PUDR = bit;
+        regs->PIO_PPDDR = bit;
+    }
+#endif
+}
+
 void
 gpio_peripheral(uint32_t gpio, char ptype, int32_t pull_up)
 {
@@ -40,11 +62,7 @@ gpio_peripheral(uint32_t gpio, char ptype, int32_t pull_up)
     regs->PIO_ABCDSR[0] = (regs->PIO_ABCDSR[0] & ~bit) | (pt & 0x01 ? bit : 0);
     regs->PIO_ABCDSR[1] = (regs->PIO_ABCDSR[1] & ~bit) | (pt & 0x02 ? bit : 0);
 #endif
-
-    if (pull_up > 0)
-        regs->PIO_PUER = bit;
-    else
-        regs->PIO_PUDR = bit;
+    set_pull_up(regs, bit, pull_up);
     regs->PIO_PDR = bit;
 }
 
@@ -78,7 +96,7 @@ gpio_out_reset(struct gpio_out g, uint8_t val)
     regs->PIO_OER = g.bit;
     regs->PIO_OWER = g.bit;
     regs->PIO_PER = g.bit;
-    regs->PIO_PUDR = g.bit;
+    set_pull_up(regs, g.bit, 0);
     irq_restore(flag);
 }
 
@@ -113,13 +131,15 @@ gpio_in_setup(uint8_t pin, int8_t pull_up)
 {
     if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
         goto fail;
+    if (CONFIG_MACH_SAM3X && pull_up < 0)
+        goto fail;
     uint32_t port = GPIO2PORT(pin);
     enable_pclock(ID_PIOA + port);
     struct gpio_in g = { .regs=digital_regs[port], .bit=GPIO2BIT(pin) };
     gpio_in_reset(g, pull_up);
     return g;
 fail:
-    shutdown("Not an input pin");
+    shutdown("Not a valid input pin");
 }
 
 void
@@ -127,10 +147,7 @@ gpio_in_reset(struct gpio_in g, int8_t pull_up)
 {
     Pio *regs = g.regs;
     irqstatus_t flag = irq_save();
-    if (pull_up)
-        regs->PIO_PUER = g.bit;
-    else
-        regs->PIO_PUDR = g.bit;
+    set_pull_up(regs, g.bit, pull_up);
     regs->PIO_ODR = g.bit;
     regs->PIO_PER = g.bit;
     irq_restore(flag);
diff --git a/src/avr/gpio.c b/src/avr/gpio.c
index c7ca1220..6ff21c26 100644
--- a/src/avr/gpio.c
+++ b/src/avr/gpio.c
@@ -74,7 +74,7 @@ gpio_out_write(struct gpio_out g, uint8_t val)
 struct gpio_in
 gpio_in_setup(uint8_t pin, int8_t pull_up)
 {
-    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
+    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs) || pull_up < 0)
         goto fail;
     struct gpio_digital_regs *regs = GPIO2REGS(pin);
     if (! regs)
@@ -83,7 +83,7 @@ gpio_in_setup(uint8_t pin, int8_t pull_up)
     gpio_in_reset(g, pull_up);
     return g;
 fail:
-    shutdown("Not an input pin");
+    shutdown("Not a valid input pin");
 }
 
 void
diff --git a/src/lpc176x/gpio.c b/src/lpc176x/gpio.c
index 0b5fb1a9..5c76ec55 100644
--- a/src/lpc176x/gpio.c
+++ b/src/lpc176x/gpio.c
@@ -23,7 +23,7 @@ static LPC_GPIO_TypeDef * const digital_regs[] = {
 
 // Set the mode and extended function of a pin
 void
-gpio_peripheral(uint32_t gpio, int func, int pullup)
+gpio_peripheral(uint32_t gpio, int func, int pull_up)
 {
     uint32_t bank_pos = GPIO2PORT(gpio) * 2, pin_pos = (gpio % 32) * 2;
     if (pin_pos >= 32) {
@@ -31,12 +31,12 @@ gpio_peripheral(uint32_t gpio, int func, int pullup)
         bank_pos++;
     }
     uint32_t sel_bits = (func & 0x03) << pin_pos, mask = ~(0x03 << pin_pos);
-    uint32_t mode_bits = (pullup ? 0x00 : 0x02) << pin_pos;
+    uint32_t mode = (pull_up ? (pull_up > 0 ? 0x00 : 0x03) : 0x02) << pin_pos;
     volatile uint32_t *pinsel = &LPC_PINCON->PINSEL0;
     volatile uint32_t *pinmode = &LPC_PINCON->PINMODE0;
     irqstatus_t flag = irq_save();
     pinsel[bank_pos] = (pinsel[bank_pos] & mask) | sel_bits;
-    pinmode[bank_pos] = (pinmode[bank_pos] & mask) | mode_bits;
+    pinmode[bank_pos] = (pinmode[bank_pos] & mask) | mode;
     irq_restore(flag);
 }
 
diff --git a/src/stm32f1/gpio.c b/src/stm32f1/gpio.c
index e6df3888..ed950461 100644
--- a/src/stm32f1/gpio.c
+++ b/src/stm32f1/gpio.c
@@ -114,7 +114,8 @@ gpio_in_reset(struct gpio_in g, int8_t pull_up)
     irqstatus_t flag = irq_save();
     if (pull_up) {
         LL_GPIO_SetPinMode(g.regs, g.bit, LL_GPIO_MODE_INPUT);
-        LL_GPIO_SetPinPull(g.regs, g.bit, LL_GPIO_PULL_UP);
+        uint32_t p = pull_up > 0 ? LL_GPIO_PULL_UP : LL_GPIO_PULL_DOWN;
+        LL_GPIO_SetPinPull(g.regs, g.bit, p);
     } else {
         LL_GPIO_SetPinMode(g.regs, g.bit, LL_GPIO_MODE_FLOATING);
     }
diff --git a/src/tmcuart.c b/src/tmcuart.c
index 82846b88..e4b04cb8 100644
--- a/src/tmcuart.c
+++ b/src/tmcuart.c
@@ -176,7 +176,7 @@ command_config_tmcuart(uint32_t *args)
                                     , sizeof(*t));
     uint8_t pull_up = args[2];
     uint32_t rx_pin = args[1], tx_pin = args[3];
-    t->rx_pin = gpio_in_setup(rx_pin, pull_up);
+    t->rx_pin = gpio_in_setup(rx_pin, !!pull_up);
     t->tx_pin = gpio_out_setup(tx_pin, 1);
     t->cfg_bit_time = args[4];
     t->flags = (TU_LINE_HIGH | (pull_up ? TU_PULLUP : 0)