diff --git a/platform/hw_utils.c b/platform/hw_utils.c
index 876b280..7619775 100644
--- a/platform/hw_utils.c
+++ b/platform/hw_utils.c
@@ -240,34 +240,45 @@ char * pinmask2str_up(uint32_t pins, char *buffer)
     return buffer;
 }
 
-/** Spread packed port pins using a mask */
-uint32_t pinmask_spread(uint32_t packed, uint32_t mask)
+/** spread a packed pinfield using a mask */
+uint32_t pinmask_spread_32(uint32_t packed, uint32_t mask)
 {
     uint32_t result = 0;
     uint32_t poke = 1;
+    if(packed == 0) return 0;
+
     for (int i = 0; i<32; i++) {
-        if (mask & (1<<i)) {
+        if (mask & 1) {
             if (packed & poke) {
                 result |= 1<<i;
+                packed ^= poke;
+                if (packed == 0) break;
             }
             poke <<= 1;
         }
+        mask >>= 1;
+        // if (mask == 0) break;
     }
+
     return result;
 }
 
 /** Pack spread port pins using a mask */
-uint32_t pinmask_pack(uint32_t spread, uint32_t mask)
+uint32_t pinmask_pack_32(uint32_t spread, uint32_t mask)
 {
     uint32_t result = 0;
     uint32_t poke = 1;
     for (int i = 0; i<32; i++) {
-        if (mask & (1<<i)) {
+        if (mask & 1) {
             if (spread & (1<<i)) {
                 result |= poke;
+                spread ^= (1<<i);
+                if (spread == 0) break;
             }
             poke <<= 1;
         }
+        mask >>= 1;
+        // if (mask == 0) break;
     }
     return result;
 }
diff --git a/platform/hw_utils.h b/platform/hw_utils.h
index 8577cff..8fec5d6 100644
--- a/platform/hw_utils.h
+++ b/platform/hw_utils.h
@@ -98,7 +98,13 @@ char * pinmask2str_up(uint32_t pins, char *buffer);
  * @param mask - positions of the bits (eg. 0x8803)
  * @return - bits spread to their positions (always counting from right)
  */
-uint32_t pinmask_spread(uint32_t packed, uint32_t mask);
+uint32_t pinmask_spread_32(uint32_t packed, uint32_t mask);
+
+/** Spread packed port pins using a mask - 16-bit version */
+static inline uint16_t pinmask_spread(uint16_t packed, uint16_t mask)
+{
+    return (uint16_t) pinmask_spread_32(packed, mask);
+}
 
 /**
  * Pack spread port pins using a mask
@@ -107,7 +113,13 @@ uint32_t pinmask_spread(uint32_t packed, uint32_t mask);
  * @param mask - mask of the bits we want to pack (eg. 0x8803)
  * @return - packed bits, right aligned (eg. 0b1110)
  */
-uint32_t pinmask_pack(uint32_t spread, uint32_t mask);
+uint32_t pinmask_pack_32(uint32_t spread, uint32_t mask);
+
+/** Pack spread port pins using a mask - 16-bit version */
+static inline uint16_t pinmask_pack(uint32_t spread, uint32_t mask)
+{
+    return (uint16_t) pinmask_pack_32(spread, mask);
+}
 
 /**
  * Convert spread port pin number to a packed index using a mask
diff --git a/units/digital_out/_dout_settings.c b/units/digital_out/_dout_settings.c
index f275504..99cc1b3 100644
--- a/units/digital_out/_dout_settings.c
+++ b/units/digital_out/_dout_settings.c
@@ -47,13 +47,13 @@ error_t DOut_loadIni(Unit *unit, const char *key, const char *value)
         suc = parse_port_name(value, &priv->port_name);
     }
     else if (streq(key, "pins")) {
-        priv->pins = parse_pinmask(value, &suc);
+        priv->pins = (uint16_t) parse_pinmask(value, &suc);
     }
     else if (streq(key, "initial")) {
-        priv->initial = parse_pinmask(value, &suc);
+        priv->initial = (uint16_t) parse_pinmask(value, &suc);
     }
     else if (streq(key, "open-drain")) {
-        priv->open_drain = parse_pinmask(value, &suc);
+        priv->open_drain = (uint16_t) parse_pinmask(value, &suc);
     }
     else {
         return E_BAD_KEY;
diff --git a/units/sipo/_sipo_api.c b/units/sipo/_sipo_api.c
new file mode 100644
index 0000000..e5c0a3c
--- /dev/null
+++ b/units/sipo/_sipo_api.c
@@ -0,0 +1,11 @@
+//
+// Created by MightyPork on 2018/02/03.
+//
+
+#include "platform.h"
+#include "unit_base.h"
+#include "unit_sipo.h"
+
+#define SIPO_INTERNAL
+#include "_sipo_internal.h"
+
diff --git a/units/sipo/_sipo_init.c b/units/sipo/_sipo_init.c
new file mode 100644
index 0000000..337f6b9
--- /dev/null
+++ b/units/sipo/_sipo_init.c
@@ -0,0 +1,123 @@
+//
+// Created by MightyPork on 2018/02/03.
+//
+
+#include "platform.h"
+#include "unit_base.h"
+
+#define SIPO_INTERNAL
+#include "_sipo_internal.h"
+
+/** Allocate data structure and set defaults */
+error_t USIPO_preInit(Unit *unit)
+{
+    struct priv *priv = unit->data = calloc_ck(1, sizeof(struct priv));
+    if (priv == NULL) return E_OUT_OF_MEM;
+
+    priv->store_pname = 'A';
+    priv->store_pnum = 0;
+    priv->store_pol = true;
+
+    priv->shift_pname = 'A';
+    priv->shift_pnum = 1;
+    priv->shift_pol = true;
+
+    priv->clear_pname = 'A';
+    priv->clear_pnum = 2;
+    priv->clear_pol = false;
+
+    priv->data_pname = 'A';
+    priv->data_pins = (1<<3);
+
+    return E_SUCCESS;
+}
+
+/** Finalize unit set-up */
+error_t USIPO_init(Unit *unit)
+{
+    bool suc = true;
+    struct priv *priv = unit->data;
+
+    // --- Parse config ---
+    priv->store_ll = hw_pin2ll(priv->store_pnum, &suc);
+    priv->store_port = hw_port2periph(priv->store_pname, &suc);
+    Resource store_rsc = hw_pin2resource(priv->store_pname, priv->store_pnum, &suc);
+    if (!suc) return E_BAD_CONFIG;
+    TRY(rsc_claim(unit, store_rsc));
+
+    priv->shift_ll = hw_pin2ll(priv->shift_pnum, &suc);
+    priv->shift_port = hw_port2periph(priv->shift_pname, &suc);
+    Resource shift_rsc = hw_pin2resource(priv->shift_pname, priv->shift_pnum, &suc);
+    if (!suc) return E_BAD_CONFIG;
+    TRY(rsc_claim(unit, shift_rsc));
+
+    priv->clear_ll = hw_pin2ll(priv->clear_pnum, &suc);
+    priv->clear_port = hw_port2periph(priv->clear_pname, &suc);
+    Resource clear_rsc = hw_pin2resource(priv->clear_pname, priv->clear_pnum, &suc);
+    if (!suc) return E_BAD_CONFIG;
+    TRY(rsc_claim(unit, clear_rsc));
+
+    // Claim all needed pins
+    TRY(rsc_claim_gpios(unit, priv->data_pname, priv->data_pins));
+    priv->data_port = hw_port2periph(priv->data_pname, &suc);
+
+    // --- Init hardware ---
+
+    priv->data_width = 0;
+    for (int i = 0; i < 16; i++) {
+        if (priv->data_pins & (1 << i)) {
+            uint32_t ll_pin = hw_pin2ll((uint8_t) i, &suc);
+            LL_GPIO_SetPinMode(priv->data_port, ll_pin, LL_GPIO_MODE_OUTPUT);
+            LL_GPIO_SetPinOutputType(priv->data_port, ll_pin, LL_GPIO_OUTPUT_PUSHPULL);
+            LL_GPIO_SetPinSpeed(priv->data_port, ll_pin, LL_GPIO_SPEED_FREQ_HIGH);
+            priv->data_width++;
+        }
+    }
+
+    // Set the initial state - zeros
+    priv->data_port->ODR &= ~priv->data_pins;
+
+
+    // STORE
+    LL_GPIO_SetPinMode(priv->store_port, priv->store_ll, LL_GPIO_MODE_OUTPUT);
+    LL_GPIO_SetPinOutputType(priv->store_port, priv->store_ll, LL_GPIO_OUTPUT_PUSHPULL);
+    LL_GPIO_SetPinSpeed(priv->store_port, priv->store_ll, LL_GPIO_SPEED_FREQ_HIGH);
+
+    if (priv->store_pol)
+        LL_GPIO_ResetOutputPin(priv->store_port, priv->store_ll);
+    else
+        LL_GPIO_SetOutputPin(priv->store_port, priv->store_ll);
+
+    // SHIFT
+    LL_GPIO_SetPinMode(priv->shift_port, priv->shift_ll, LL_GPIO_MODE_OUTPUT);
+    LL_GPIO_SetPinOutputType(priv->shift_port, priv->shift_ll, LL_GPIO_OUTPUT_PUSHPULL);
+    LL_GPIO_SetPinSpeed(priv->shift_port, priv->shift_ll, LL_GPIO_SPEED_FREQ_HIGH);
+
+    if (priv->shift_pol)
+        LL_GPIO_ResetOutputPin(priv->shift_port, priv->shift_ll);
+    else
+        LL_GPIO_SetOutputPin(priv->shift_port, priv->shift_ll);
+
+    // CLEAR
+    LL_GPIO_SetPinMode(priv->clear_port, priv->clear_ll, LL_GPIO_MODE_OUTPUT);
+    LL_GPIO_SetPinOutputType(priv->clear_port, priv->clear_ll, LL_GPIO_OUTPUT_PUSHPULL);
+    LL_GPIO_SetPinSpeed(priv->clear_port, priv->clear_ll, LL_GPIO_SPEED_FREQ_HIGH);
+
+    if (priv->clear_pol)
+        LL_GPIO_ResetOutputPin(priv->clear_port, priv->clear_ll);
+    else
+        LL_GPIO_SetOutputPin(priv->clear_port, priv->clear_ll);
+
+    return E_SUCCESS;
+}
+
+
+/** Tear down the unit */
+void USIPO_deInit(Unit *unit)
+{
+    // Release all resources, deinit pins
+    rsc_teardown(unit);
+
+    // Free memory
+    free_ck(unit->data);
+}
diff --git a/units/sipo/_sipo_internal.h b/units/sipo/_sipo_internal.h
new file mode 100644
index 0000000..3db7808
--- /dev/null
+++ b/units/sipo/_sipo_internal.h
@@ -0,0 +1,70 @@
+//
+// Created by MightyPork on 2018/02/03.
+//
+
+#ifndef GEX_F072_SIPO_INTERNAL_H
+#define GEX_F072_SIPO_INTERNAL_H
+
+#ifndef SIPO_INTERNAL
+#error bad include!
+#endif
+
+#include "unit_base.h"
+
+/** Private data structure */
+struct priv {
+    // settings
+    char    store_pname;
+    uint8_t store_pnum;
+    bool    store_pol;   //!< Store pulse active edge
+
+    char    shift_pname;
+    uint8_t shift_pnum;
+    bool    shift_pol;   //!< Shift clock active edge
+
+    char    clear_pname;
+    uint8_t clear_pnum;
+    bool    clear_pol;   //!< Clear signal active level
+
+    char     data_pname;
+    uint16_t data_pins;
+
+    // live fields
+    uint32_t store_ll;
+    uint32_t shift_ll;
+    uint32_t clear_ll;
+
+    GPIO_TypeDef *store_port;
+    GPIO_TypeDef *shift_port;
+    GPIO_TypeDef *clear_port;
+    GPIO_TypeDef *data_port;
+
+    uint8_t data_width;
+};
+
+/** Allocate data structure and set defaults */
+error_t USIPO_preInit(Unit *unit);
+
+/** Load from a binary buffer stored in Flash */
+void USIPO_loadBinary(Unit *unit, PayloadParser *pp);
+
+/** Write to a binary buffer for storing in Flash */
+void USIPO_writeBinary(Unit *unit, PayloadBuilder *pb);
+
+// ------------------------------------------------------------------------
+
+/** Parse a key-value pair from the INI file */
+error_t USIPO_loadIni(Unit *unit, const char *key, const char *value);
+
+/** Generate INI file section for the unit */
+void USIPO_writeIni(Unit *unit, IniWriter *iw);
+
+// ------------------------------------------------------------------------
+
+/** Finalize unit set-up */
+error_t USIPO_init(Unit *unit);
+
+/** Tear down the unit */
+void USIPO_deInit(Unit *unit);
+
+#endif //GEX_F072_SIPO_INTERNAL_H
diff --git a/units/sipo/_sipo_settings.c b/units/sipo/_sipo_settings.c
new file mode 100644
index 0000000..897928f
--- /dev/null
+++ b/units/sipo/_sipo_settings.c
@@ -0,0 +1,122 @@
+//
+// Created by MightyPork on 2018/02/03.
+//
+
+#include "platform.h"
+#include "unit_base.h"
+
+#define SIPO_INTERNAL
+#include "_sipo_internal.h"
+
+/** Load from a binary buffer stored in Flash */
+void USIPO_loadBinary(Unit *unit, PayloadParser *pp)
+{
+    struct priv *priv = unit->data;
+
+    uint8_t version = pp_u8(pp);
+    (void)version;
+
+    priv->store_pname = pp_char(pp);
+    priv->store_pnum = pp_u8(pp);
+    priv->store_pol = pp_bool(pp);
+
+    priv->shift_pname = pp_char(pp);
+    priv->shift_pnum = pp_u8(pp);
+    priv->shift_pol = pp_bool(pp);
+
+    priv->clear_pname = pp_char(pp);
+    priv->clear_pnum = pp_u8(pp);
+    priv->clear_pol = pp_bool(pp);
+
+    priv->data_pname = pp_char(pp);
+    priv->data_pins = pp_u16(pp);
+}
+
+/** Write to a binary buffer for storing in Flash */
+void USIPO_writeBinary(Unit *unit, PayloadBuilder *pb)
+{
+    struct priv *priv = unit->data;
+
+    pb_u8(pb, 0); // version
+
+    pb_char(pb, priv->store_pname);
+    pb_u8(pb, priv->store_pnum);
+    pb_bool(pb, priv->store_pol);
+
+    pb_char(pb, priv->shift_pname);
+    pb_u8(pb, priv->shift_pnum);
+    pb_bool(pb, priv->shift_pol);
+
+    pb_char(pb, priv->clear_pname);
+    pb_u8(pb, priv->clear_pnum);
+    pb_bool(pb, priv->clear_pol);
+
+    pb_char(pb, priv->data_pname);
+    pb_u16(pb, priv->data_pins);
+}
+
+// ------------------------------------------------------------------------
+
+/** Parse a key-value pair from the INI file */
+error_t USIPO_loadIni(Unit *unit, const char *key, const char *value)
+{
+    bool suc = true;
+    struct priv *priv = unit->data;
+
+    if (streq(key, "store-pin")) {
+        suc = parse_pin(value, &priv->store_pname, &priv->store_pnum);
+    }
+    else if (streq(key, "shift-pin")) {
+        suc = parse_pin(value, &priv->shift_pname, &priv->shift_pnum);
+    }
+    else if (streq(key, "clear-pin")) {
+        suc = parse_pin(value, &priv->clear_pname, &priv->clear_pnum);
+    }
+
+    else if (streq(key, "store-pol")) {
+        priv->store_pol = (bool) avr_atoi(value);
+    }
+    else if (streq(key, "shift-pol")) {
+        priv->shift_pol = (bool) avr_atoi(value);
+    }
+    else if (streq(key, "clear-pol")) {
+        priv->clear_pol = (bool) avr_atoi(value);
+    }
+
+    else if (streq(key, "data-port")) {
+        suc = parse_port_name(value, &priv->data_pname);
+    }
+    else if (streq(key, "data-pins")) {
+        priv->data_pins = (uint16_t) parse_pinmask(value, &suc);
+    }
+
+    else {
+        return E_BAD_KEY;
+    }
+
+    if (!suc) return E_BAD_VALUE;
+    return E_SUCCESS;
+}
+
+/** Generate INI file section for the unit */
+void USIPO_writeIni(Unit *unit, IniWriter *iw)
+{
+    struct priv *priv = unit->data;
+
+    iw_comment(iw, "Store pin & its active edge (1-rising,0-falling)");
+    iw_entry(iw, "store-pin", "%c%d", priv->store_pname,  priv->store_pnum);
+    iw_entry(iw, "store-pol", "%d", priv->store_pol);
+
+    iw_comment(iw, "Shift pin & its active edge");
+    iw_entry(iw, "shift-pin", "%c%d", priv->shift_pname,  priv->shift_pnum);
+    iw_entry(iw, "shift-pol", "%d", priv->shift_pol);
+
+    iw_comment(iw, "Clear pin & its active level");
+    iw_entry(iw, "clear-pin", "%c%d", priv->clear_pname,  priv->clear_pnum);
+    iw_entry(iw, "clear-pol", "%d", priv->clear_pol);
+
+    iw_comment(iw, "Data port and pins");
+    iw_entry(iw, "data-port", "%c", priv->data_pname);
+    iw_entry(iw, "data-pins", "%s", pinmask2str(priv->data_pins, unit_tmp512));
+}
+
diff --git a/units/sipo/unit_sipo.c b/units/sipo/unit_sipo.c
new file mode 100644
index 0000000..74aead0
--- /dev/null
+++ b/units/sipo/unit_sipo.c
@@ -0,0 +1,98 @@
+//
+// Created by MightyPork on 2017/11/25.
+//
+
+#include "unit_base.h"
+#include "unit_sipo.h"
+
+#define SIPO_INTERNAL
+
+#include "_sipo_internal.h"
+
+error_t UU_SIPO_Write(Unit *unit, const uint8_t *buffer, uint16_t buflen)
+{
+    struct priv *priv = unit->data;
+
+    if (buflen % priv->data_width != 0) {
+        return E_BAD_COUNT; // must be a multiple of the channel count
+    }
+
+    // buffer contains data for the individual data pins, back to back as AAA BBB CCC (whole bytes)
+
+    const uint16_t bytelen = buflen / priv->data_width;
+
+    for (int bn = 0; bn < bytelen; bn--) {
+        // send the byte
+        for (int i = 0; i < 8; i++) {
+            uint16_t packed = 0;
+
+            for (int j = 0; j < priv->data_width; j++) {
+                packed |= (bool) (buffer[bn + j * bytelen] & (1 << i));
+                packed <<= 1;
+            }
+
+            uint16_t spread = pinmask_spread(packed, priv->data_pins);
+            uint16_t set = spread;
+            uint16_t reset = ((~spread) & priv->data_pins);
+            priv->data_port->BSRR = set | (reset << 16);
+
+            if (priv->shift_pol) {
+                LL_GPIO_SetOutputPin(priv->shift_port, priv->shift_ll);
+                LL_GPIO_ResetOutputPin(priv->shift_port, priv->shift_ll);
+            }
+            else {
+                LL_GPIO_ResetOutputPin(priv->shift_port, priv->shift_ll);
+                LL_GPIO_SetOutputPin(priv->shift_port, priv->shift_ll);
+            }
+        }
+    }
+
+    if (priv->store_pol) {
+        LL_GPIO_SetOutputPin(priv->store_port, priv->store_ll);
+        LL_GPIO_ResetOutputPin(priv->store_port, priv->store_ll);
+    }
+    else {
+        LL_GPIO_ResetOutputPin(priv->store_port, priv->store_ll);
+        LL_GPIO_SetOutputPin(priv->store_port, priv->store_ll);
+    }
+}
+
+// ------------------------------------------------------------------------
+
+enum SipoCmd_ {
+    CMD_WRITE,
+};
+
+/** Handle a request message */
+static error_t USIPO_handleRequest(Unit *unit, TF_ID frame_id, uint8_t command, PayloadParser *pp)
+{
+    switch (command) {
+        case CMD_WRITE:;
+            uint32_t len;
+            const uint8_t *tail = pp_tail(pp, &len);
+            UU_SIPO_Write(unit, (uint8_t *) tail, (uint16_t) len);
+            return E_SUCCESS;
+
+        default:
+            return E_UNKNOWN_COMMAND;
+    }
+}
+
+// ------------------------------------------------------------------------
+
+/** Unit template */
+const UnitDriver UNIT_SIPO = {
+    .name = "SIPO",
+    .description = "Shift register driver (595, 4094)",
+    // Settings
+    .preInit = USIPO_preInit,
+    .cfgLoadBinary = USIPO_loadBinary,
+    .cfgWriteBinary = USIPO_writeBinary,
+    .cfgLoadIni = USIPO_loadIni,
+    .cfgWriteIni = USIPO_writeIni,
+    // Init
+    .init = USIPO_init,
+    .deInit = USIPO_deInit,
+    // Function
+    .handleRequest = USIPO_handleRequest,
+};
diff --git a/units/sipo/unit_sipo.h b/units/sipo/unit_sipo.h
new file mode 100644
index 0000000..498a040
--- /dev/null
+++ b/units/sipo/unit_sipo.h
@@ -0,0 +1,16 @@
+//
+// Created by MightyPork on 2017/11/25.
+//
+// Digital input unit; single or multiple pin read access on one port (A-F)
+//
+
+#ifndef U_SIPO_H
+#define U_SIPO_H
+
+#include "unit.h"
+
+extern const UnitDriver UNIT_SIPO;
+
+// UU_ prototypes
+
+#endif //U_SIPO_H