diff --git a/framework/resources.c b/framework/resources.c
index 9ad8192..7c66a87 100644
--- a/framework/resources.c
+++ b/framework/resources.c
@@ -5,6 +5,7 @@
 #include "platform.h"
 #include "unit.h"
 #include "resources.h"
+#include "pin_utils.h"
 
 static bool rsc_initialized = false;
 
@@ -82,6 +83,30 @@ bool rsc_claim_range(Unit *unit, Resource rsc0, Resource rsc1)
     return true;
 }
 
+bool rsc_claim_gpios(Unit *unit, char port_name, uint16_t pins)
+{
+    bool suc = true;
+
+    for (int i = 0; i < 16; i++) {
+        if (pins & (1 << i)) {
+            Resource rsc = pin2resource(port_name, (uint8_t) i, &suc);
+            if (!suc) {
+                unit->status = E_BAD_CONFIG;
+
+                rsc_teardown(unit);
+                return false;
+            }
+
+            suc = rsc_claim(unit, rsc);
+            if (!suc) {
+                rsc_teardown(unit);
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 /**
  * Free a resource for other use
  *
diff --git a/framework/resources.h b/framework/resources.h
index 54285c7..4ecb400 100644
--- a/framework/resources.h
+++ b/framework/resources.h
@@ -88,4 +88,15 @@ void rsc_teardown(Unit *unit);
 void rsc_free(Unit *unit, Resource rsc);
 void rsc_free_range(Unit *unit, Resource rsc0, Resource rsc1);
 
+/**
+ * Claim GPIOs by bitmask and port name, atomically.
+ * Tear down the unit on failure.
+ *
+ * @param unit - claiming unit
+ * @param port_name - port (eg. 'A')
+ * @param pins - pins, bitmask
+ * @return success
+ */
+bool rsc_claim_gpios(Unit *unit, char port_name, uint16_t pins);
+
 #endif //GEX_RESOURCES_H
diff --git a/framework/settings.c b/framework/settings.c
index 45ec1f9..fd74770 100644
--- a/framework/settings.c
+++ b/framework/settings.c
@@ -16,7 +16,7 @@ static bool savebuf_ovhandler(PayloadBuilder *pb, uint32_t more);
 
 // This is the first entry in a valid config.
 // Change with each breaking change to force config reset.
-#define CONFIG_MARKER 0xA55D
+#define CONFIG_MARKER 0xA55E
 
 void settings_load(void)
 {
@@ -270,7 +270,7 @@ void settings_load_ini_begin(void)
 
 void settings_load_ini_key(const char *restrict section, const char *restrict key, const char *restrict value)
 {
-    dbg("[%s] %s = %s", section, key, value);
+//    dbg("[%s] %s = %s", section, key, value);
     static char namebuf[INI_KEY_MAX];
 
     if (streq(section, "SYSTEM")) {
diff --git a/framework/unit.c b/framework/unit.c
index 1b57d5e..5e20cca 100644
--- a/framework/unit.c
+++ b/framework/unit.c
@@ -6,6 +6,8 @@
 #include "unit.h"
 #include "resources.h"
 
+char unit_tmp64[64];
+
 // Abort partly inited unit
 void clean_failed_unit(Unit *unit)
 {
diff --git a/framework/unit.h b/framework/unit.h
index 0f789e6..bb85589 100644
--- a/framework/unit.h
+++ b/framework/unit.h
@@ -11,6 +11,8 @@
 #include "utils/payload_builder.h"
 #include "utils/payload_parser.h"
 
+extern char unit_tmp64[64]; // temporary static buffer
+
 typedef struct unit Unit;
 typedef struct unit_driver UnitDriver;
 
diff --git a/gex.mk b/gex.mk
index e4505d0..5c5c8f2 100644
--- a/gex.mk
+++ b/gex.mk
@@ -10,6 +10,7 @@ GEX_SRC_DIR = \
     User/units/test \
     User/units/pin \
     User/units/digital_out \
+    User/units/digital_in \
     User/TinyFrame \
     User/CWPack \
     User/tasks
diff --git a/platform/plat_compat.h b/platform/plat_compat.h
index 1a64d8a..f64adb9 100644
--- a/platform/plat_compat.h
+++ b/platform/plat_compat.h
@@ -45,13 +45,20 @@
 
 // -------- Platform specific includes and defines ---------
 
+/// Feature flags:
+// PLAT_FLASHBANKS - has the Banks field on the Flash config struct
+// PLAT_NO_FLOATING_INPUTS - can't have digital inputs with no pull resistor
+// PLAT_USB_PHYCLOCK - requires special config of phy clock for USB
+// PLAT_USB_OTGFS - uses the USB OTG IP, needs different config code
+
 #if defined(GEX_PLAT_F103_BLUEPILL)
 
     // platform name for the version string
     #define GEX_PLATFORM "STM32F103-Bluepill"
 
-    // This platform has the Banks field on the Flash config struct for settings save
+    // feature flags
     #define PLAT_FLASHBANKS 1
+    #define PLAT_NO_FLOATING_INPUTS 1
 
     #include <stm32f1xx.h>
     #include <stm32f1xx_hal.h>
diff --git a/platform/platform.c b/platform/platform.c
index de3420c..7a718c4 100644
--- a/platform/platform.c
+++ b/platform/platform.c
@@ -10,6 +10,7 @@
 
 #include "units/pin/unit_pin.h"
 #include "units/digital_out/unit_dout.h"
+#include "units/digital_in/unit_din.h"
 #include "units/neopixel/unit_neopixel.h"
 #include "units/test/unit_test.h"
 
@@ -24,6 +25,7 @@ void plat_init_resources(void)
     // --- Common unit drivers ---
     ureg_add_type(&UNIT_PIN);
     ureg_add_type(&UNIT_DOUT);
+    ureg_add_type(&UNIT_DIN);
 
     #if HAVE_TEST_UNIT
         ureg_add_type(&UNIT_TEST);
diff --git a/units/digital_in/unit_din.c b/units/digital_in/unit_din.c
new file mode 100644
index 0000000..cb3972a
--- /dev/null
+++ b/units/digital_in/unit_din.c
@@ -0,0 +1,237 @@
+//
+// Created by MightyPork on 2017/11/25.
+//
+
+#include <stm32f072xb.h>
+#include "comm/messages.h"
+#include "unit_base.h"
+#include "unit_din.h"
+
+/** Private data structure */
+struct priv {
+    char port_name;
+    uint16_t pins; // pin mask
+    uint16_t pulldown; // pull-downs (default is pull-up)
+    uint16_t pullup; // pull-ups
+
+    GPIO_TypeDef *port;
+};
+
+// ------------------------------------------------------------------------
+
+/** Load from a binary buffer stored in Flash */
+static void DI_loadBinary(Unit *unit, PayloadParser *pp)
+{
+    struct priv *priv = unit->data;
+
+    uint8_t version = pp_u8(pp);
+    (void)version;
+
+    priv->port_name = pp_char(pp);
+    priv->pins = pp_u16(pp);
+    priv->pulldown = pp_u16(pp);
+    priv->pullup = pp_u16(pp);
+
+    dbg("load bin, pulldown = %X", priv->pulldown);
+}
+
+/** Write to a binary buffer for storing in Flash */
+static void DI_writeBinary(Unit *unit, PayloadBuilder *pb)
+{
+    struct priv *priv = unit->data;
+
+    pb_u8(pb, 0); // version
+
+    pb_char(pb, priv->port_name);
+    pb_u16(pb, priv->pins);
+    pb_u16(pb, priv->pulldown);
+    pb_u16(pb, priv->pullup);
+}
+
+// ------------------------------------------------------------------------
+
+/** Parse a key-value pair from the INI file */
+static bool DI_loadIni(Unit *unit, const char *key, const char *value)
+{
+    bool suc = true;
+    struct priv *priv = unit->data;
+
+    if (streq(key, "port")) {
+        suc = parse_port(value, &priv->port_name);
+    }
+    else if (streq(key, "pins")) {
+        priv->pins = parse_pinmask(value, &suc);
+    }
+    else if (streq(key, "pull-up")) {
+        priv->pullup = parse_pinmask(value, &suc);
+    }
+    else if (streq(key, "pull-down")) {
+        priv->pulldown = parse_pinmask(value, &suc);
+        dbg("parsinf ini, pulldown = %X", priv->pulldown);
+    }
+    else {
+        return false;
+    }
+
+    return suc;
+}
+
+/** Generate INI file section for the unit */
+static void DI_writeIni(Unit *unit, IniWriter *iw)
+{
+    struct priv *priv = unit->data;
+
+    iw_comment(iw, "Port name");
+    iw_entry(iw, "port", "%c", priv->port_name);
+
+    iw_comment(iw, "Pins (comma separated, supports ranges)");
+    iw_entry(iw, "pins", "%s", str_pinmask(priv->pins, unit_tmp64));
+
+    iw_comment(iw, "Pins with pull-up");
+    iw_entry(iw, "pull-up", "%s", str_pinmask(priv->pullup, unit_tmp64));
+
+    iw_comment(iw, "Pins with pull-down");
+    iw_entry(iw, "pull-down", "%s", str_pinmask(priv->pulldown, unit_tmp64));
+
+#if PLAT_NO_FLOATING_INPUTS
+    iw_comment(iw, "NOTE: Pins use pull-up by default.\r\n");
+#endif
+}
+
+// ------------------------------------------------------------------------
+
+/** Allocate data structure and set defaults */
+static bool DI_preInit(Unit *unit)
+{
+    bool suc = true;
+    struct priv *priv = unit->data = calloc_ck(1, sizeof(struct priv), &suc);
+    CHECK_SUC();
+
+    // some defaults
+    priv->port_name = 'A';
+    priv->pins = 0x0001;
+    priv->pulldown = 0x0000;
+    priv->pullup = 0x0000;
+
+    return true;
+}
+
+/** Finalize unit set-up */
+static bool DI_init(Unit *unit)
+{
+    bool suc = true;
+    struct priv *priv = unit->data;
+
+    priv->pulldown &= priv->pins;
+    priv->pullup &= priv->pins;
+
+    // --- Parse config ---
+    priv->port = port2periph(priv->port_name, &suc);
+    if (!suc) {
+        unit->status = E_BAD_CONFIG;
+        return false;
+    }
+
+    // Claim all needed pins
+    suc = rsc_claim_gpios(unit, priv->port_name, priv->pins);
+    CHECK_SUC();
+
+    uint16_t mask = 1;
+    for (int i = 0; i < 16; i++, mask <<= 1) {
+        if (priv->pins & mask) {
+            uint32_t ll_pin = pin2ll((uint8_t) i, &suc);
+
+            // --- Init hardware ---
+            LL_GPIO_SetPinMode(priv->port, ll_pin, LL_GPIO_MODE_INPUT);
+
+            uint32_t pull = 0;
+
+            #if PLAT_NO_FLOATING_INPUTS
+                pull = LL_GPIO_PULL_UP;
+            #else
+                pull = LL_GPIO_PULL_NO;
+            #endif
+
+            if (priv->pulldown & mask) pull = LL_GPIO_PULL_DOWN;
+            if (priv->pullup & mask) pull = LL_GPIO_PULL_UP;
+            LL_GPIO_SetPinPull(priv->port, ll_pin, pull);
+        }
+    }
+
+    return true;
+}
+
+
+/** Tear down the unit */
+static void DI_deInit(Unit *unit)
+{
+    struct priv *priv = unit->data;
+
+    bool suc = true;
+    uint16_t mask = 1;
+    for (int i = 0; i < 16; i++, mask <<= 1) {
+        if (priv->pins & mask) {
+            uint32_t ll_pin = pin2ll((uint8_t) i, &suc);
+            assert_param(suc); // this should never fail if we got this far
+
+            // configure the pin as analog
+            LL_GPIO_SetPinMode(priv->port, ll_pin, LL_GPIO_MODE_ANALOG);
+        }
+    }
+
+    // Release all resources
+    rsc_teardown(unit);
+
+    // Free memory
+    free(unit->data);
+    unit->data = NULL;
+}
+
+// ------------------------------------------------------------------------
+
+enum PinCmd_ {
+    CMD_READ = 0,
+};
+
+/** Handle a request message */
+static bool DI_handleRequest(Unit *unit, TF_ID frame_id, uint8_t command, PayloadParser *pp)
+{
+    (void)pp;
+
+    struct priv *priv = unit->data;
+
+    uint16_t packed = port_pack((uint16_t) priv->port->IDR, priv->pins);
+
+    switch (command) {
+        case CMD_READ:;
+            PayloadBuilder pb = pb_start((uint8_t*)unit_tmp64, 64, NULL);
+            pb_u16(&pb, packed);
+            com_respond_buf(frame_id, MSG_SUCCESS, (uint8_t *) unit_tmp64, pb_length(&pb));
+            break;
+
+        default:
+            com_respond_bad_cmd(frame_id);
+            return false;
+    }
+
+    return true;
+}
+
+// ------------------------------------------------------------------------
+
+/** Unit template */
+const UnitDriver UNIT_DIN = {
+    .name = "DI",
+    .description = "Digital input",
+    // Settings
+    .preInit = DI_preInit,
+    .cfgLoadBinary = DI_loadBinary,
+    .cfgWriteBinary = DI_writeBinary,
+    .cfgLoadIni = DI_loadIni,
+    .cfgWriteIni = DI_writeIni,
+    // Init
+    .init = DI_init,
+    .deInit = DI_deInit,
+    // Function
+    .handleRequest = DI_handleRequest,
+};
diff --git a/units/digital_in/unit_din.h b/units/digital_in/unit_din.h
new file mode 100644
index 0000000..ecb3261
--- /dev/null
+++ b/units/digital_in/unit_din.h
@@ -0,0 +1,12 @@
+//
+// Created by MightyPork on 2017/11/25.
+//
+
+#ifndef U_DIN_H
+#define U_DIN_H
+
+#include "unit.h"
+
+extern const UnitDriver UNIT_DIN;
+
+#endif //U_DIN_H
diff --git a/units/digital_out/unit_dout.c b/units/digital_out/unit_dout.c
index fe92e7c..a331c28 100644
--- a/units/digital_out/unit_dout.c
+++ b/units/digital_out/unit_dout.c
@@ -23,6 +23,9 @@ static void DO_loadBinary(Unit *unit, PayloadParser *pp)
 {
     struct priv *priv = unit->data;
 
+    uint8_t version = pp_u8(pp);
+    (void)version;
+
     priv->port_name = pp_char(pp);
     priv->pins = pp_u16(pp);
     priv->initial = pp_u16(pp);
@@ -34,6 +37,8 @@ static void DO_writeBinary(Unit *unit, PayloadBuilder *pb)
 {
     struct priv *priv = unit->data;
 
+    pb_u8(pb, 0); // version
+
     pb_char(pb, priv->port_name);
     pb_u16(pb, priv->pins);
     pb_u16(pb, priv->initial);
@@ -71,19 +76,18 @@ static bool DO_loadIni(Unit *unit, const char *key, const char *value)
 static void DO_writeIni(Unit *unit, IniWriter *iw)
 {
     struct priv *priv = unit->data;
-    char buf[64];
 
     iw_comment(iw, "Port name");
     iw_entry(iw, "port", "%c", priv->port_name);
 
     iw_comment(iw, "Pins (comma separated, supports ranges)");
-    iw_entry(iw, "pins", "%s", str_pinmask(priv->pins, buf));
+    iw_entry(iw, "pins", "%s", str_pinmask(priv->pins, unit_tmp64));
 
     iw_comment(iw, "Initially high pins");
-    iw_entry(iw, "initial", "%s", str_pinmask(priv->initial, buf));
+    iw_entry(iw, "initial", "%s", str_pinmask(priv->initial, unit_tmp64));
 
     iw_comment(iw, "Open-drain pins");
-    iw_entry(iw, "opendrain", "%s", str_pinmask(priv->open_drain, buf));
+    iw_entry(iw, "opendrain", "%s", str_pinmask(priv->open_drain, unit_tmp64));
 }
 
 // ------------------------------------------------------------------------
@@ -120,28 +124,9 @@ static bool DO_init(Unit *unit)
         return false;
     }
 
-    dbg("Claim rsc");
-
     // Claim all needed pins
-    for (int i = 0; i < 16; i++) {
-        if (priv->pins & (1 << i)) {
-            Resource rsc = pin2resource(priv->port_name, (uint8_t) i, &suc);
-            if (!suc) {
-                unit->status = E_BAD_CONFIG;
-
-                rsc_teardown(unit);
-                return false;
-            }
-
-            suc = rsc_claim(unit, rsc);
-            if (!suc) {
-                rsc_teardown(unit);
-                return false;
-            }
-        }
-    }
-
-    dbg("Init pins");
+    suc = rsc_claim_gpios(unit, priv->port_name, priv->pins);
+    CHECK_SUC();
 
     uint16_t mask = 1;
     for (int i = 0; i < 16; i++, mask <<= 1) {
diff --git a/utils/payload_builder.h b/utils/payload_builder.h
index 86331fd..4c24aa2 100644
--- a/utils/payload_builder.h
+++ b/utils/payload_builder.h
@@ -62,7 +62,7 @@ struct PayloadBuilder_ {
 // --- utilities ---
 
 /** Get already used bytes count */
-#define pb_length(pb) ((pb)->current - (pb)->start)
+#define pb_length(pb) ((uint32_t)((pb)->current - (pb)->start))
 
 /** Reset the current pointer to start */
 #define pb_rewind(pb) do { pb->current = pb->start; } while (0)