diff --git a/lib/pbio/drv/ioport/ioport_lpf2.c b/lib/pbio/drv/ioport/ioport_lpf2.c
index 8cea8ed1d..8c7e02ad8 100644
--- a/lib/pbio/drv/ioport/ioport_lpf2.c
+++ b/lib/pbio/drv/ioport/ioport_lpf2.c
@@ -62,7 +62,7 @@ static const basic_info_t basic_infos[] = {
         },
         .mode = {
             .num_values = 1,
-            .data_type = PBIO_IODEV_DATA_TYPE_INT8,
+            .data_type = PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE,
         },
     },
     [PBIO_IODEV_TYPE_ID_LPF2_TRAIN] = {
@@ -73,7 +73,7 @@ static const basic_info_t basic_infos[] = {
         },
         .mode = {
             .num_values = 1,
-            .data_type = PBIO_IODEV_DATA_TYPE_INT8,
+            .data_type = PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE,
         },
     },
     [PBIO_IODEV_TYPE_ID_LPF2_LIGHT] = {
@@ -84,7 +84,7 @@ static const basic_info_t basic_infos[] = {
         },
         .mode = {
             .num_values = 1,
-            .data_type = PBIO_IODEV_DATA_TYPE_INT8,
+            .data_type = PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE,
         },
     },
     [PBIO_IODEV_TYPE_ID_LPF2_LIGHT1] = {
@@ -95,7 +95,7 @@ static const basic_info_t basic_infos[] = {
         },
         .mode = {
             .num_values = 1,
-            .data_type = PBIO_IODEV_DATA_TYPE_INT8,
+            .data_type = PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE,
         },
     },
     [PBIO_IODEV_TYPE_ID_LPF2_LIGHT2] = {
@@ -106,7 +106,7 @@ static const basic_info_t basic_infos[] = {
         },
         .mode = {
             .num_values = 1,
-            .data_type = PBIO_IODEV_DATA_TYPE_INT8,
+            .data_type = PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE,
         },
     },
 };
diff --git a/lib/pbio/include/pbio/iodev.h b/lib/pbio/include/pbio/iodev.h
index b2f2cc8ef..5515e791d 100644
--- a/lib/pbio/include/pbio/iodev.h
+++ b/lib/pbio/include/pbio/iodev.h
@@ -159,6 +159,12 @@ typedef enum {
     PBIO_IODEV_DATA_TYPE_FLOAT = LUMP_DATA_TYPE_DATAF,
 } pbio_iodev_data_type_t;
 
+// Bit mask for pbio_iodev_data_type_t
+#define PBIO_IODEV_DATA_TYPE_MASK (0x03)
+
+// Third bit indicates whether the mode supports writing
+#define PBIO_IODEV_DATA_TYPE_WRITABLE (0x04)
+
 /**
  * The maximum number of modes a I/O device can have.
  */
@@ -259,7 +265,7 @@ typedef struct {
      */
     uint8_t num_values;
     /**
-     * The binary format of the data for this mode.
+     * The binary format of the data for this mode and writability flag.
      */
     pbio_iodev_data_type_t data_type;
 } pbio_iodev_mode_t;
diff --git a/lib/pbio/src/iodev.c b/lib/pbio/src/iodev.c
index 954ac5aad..645e260bf 100644
--- a/lib/pbio/src/iodev.c
+++ b/lib/pbio/src/iodev.c
@@ -14,7 +14,7 @@
  * @return                  The size of the type or 0 if the type was not valid
  */
 size_t pbio_iodev_size_of(pbio_iodev_data_type_t type) {
-    switch (type) {
+    switch (type & PBIO_IODEV_DATA_TYPE_MASK) {
         case PBIO_IODEV_DATA_TYPE_INT8:
             return 1;
         case PBIO_IODEV_DATA_TYPE_INT16:
diff --git a/lib/pbio/src/uartdev.c b/lib/pbio/src/uartdev.c
index bff341b01..32beb66a2 100644
--- a/lib/pbio/src/uartdev.c
+++ b/lib/pbio/src/uartdev.c
@@ -491,12 +491,12 @@ static void pbio_uartdev_parse_msg(uartdev_port_data_t *data) {
                         goto err;
                     }
 
-                    // Check that mode supports writing.
-                    if (data->rx_msg[3]) {
-                        // TODO: Store write capability
-                    }
+                    // Mode supports writing if rx_msg[3] is nonzero. Store in 3rd bit of data type.
+                    data->info->mode_info[mode].data_type = (data->rx_msg[3] != 0) << 2;
 
                     debug_pr("mapping: in %02x out %02x\n", data->rx_msg[2], data->rx_msg[3]);
+                    debug_pr("mapping: in %02x out %02x\n", data->rx_msg[2], data->rx_msg[3]);
+                    debug_pr("Writable: %d\n", data->info->mode_info[mode].data_type & PBIO_IODEV_DATA_TYPE_WRITABLE);
 
                     break;
                 case LUMP_INFO_MODE_COMBOS:
@@ -555,13 +555,14 @@ static void pbio_uartdev_parse_msg(uartdev_port_data_t *data) {
                         DBG_ERR(data->last_err = "Did not receive all required INFO");
                         goto err;
                     }
-                    data->info->mode_info[mode].data_type = data->rx_msg[3];
+                    // Mode writability has been set previously. Now OR with mode type.
+                    data->info->mode_info[mode].data_type |= data->rx_msg[3];
                     if (data->new_mode) {
                         data->new_mode--;
                     }
 
                     debug_pr("num_values: %d\n", data->info->mode_info[mode].num_values);
-                    debug_pr("data_type: %d\n", data->info->mode_info[mode].data_type);
+                    debug_pr("data_type: %d\n", data->info->mode_info[mode].data_type & PBIO_IODEV_DATA_TYPE_MASK);
 
                     break;
             }
@@ -1093,8 +1094,7 @@ static pbio_error_t ev3_uart_set_data_begin(pbio_iodev_t *iodev, const uint8_t *
     uint8_t size;
 
     // not all modes support setting data
-    bool writable = 0; // TODO: Check write capability
-    if (!writable) {
+    if (!(mode->data_type & PBIO_IODEV_DATA_TYPE_WRITABLE)) {
         return PBIO_ERROR_INVALID_OP;
     }
 
diff --git a/lib/pbio/test/src/uartdev.c b/lib/pbio/test/src/uartdev.c
index 9a5d9366b..de56efabb 100644
--- a/lib/pbio/test/src/uartdev.c
+++ b/lib/pbio/test/src/uartdev.c
@@ -376,13 +376,13 @@ static PT_THREAD(test_boost_color_distance_sensor(struct pt *pt)) {
     tt_want_uint_op(iodev->info->mode_info[4].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
 
     tt_want_uint_op(iodev->info->mode_info[5].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[5].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[5].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[6].num_values, ==, 3);
     tt_want_uint_op(iodev->info->mode_info[6].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
 
     tt_want_uint_op(iodev->info->mode_info[7].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[7].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
+    tt_want_uint_op(iodev->info->mode_info[7].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[8].num_values, ==, 4);
     tt_want_uint_op(iodev->info->mode_info[8].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
@@ -608,7 +608,7 @@ static PT_THREAD(test_boost_interactive_motor(struct pt *pt)) {
     tt_want_uint_op(iodev->mode, ==, 0);
 
     tt_want_uint_op(iodev->info->mode_info[0].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[1].num_values, ==, 1);
     tt_want_uint_op(iodev->info->mode_info[1].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
@@ -811,16 +811,16 @@ static PT_THREAD(test_technic_large_motor(struct pt *pt)) {
     tt_want_uint_op(iodev->mode, ==, 0);
 
     tt_want_uint_op(iodev->info->mode_info[0].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[1].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[1].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[1].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[2].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[2].data_type, ==, PBIO_IODEV_DATA_TYPE_INT32);
+    tt_want_uint_op(iodev->info->mode_info[2].data_type, ==, PBIO_IODEV_DATA_TYPE_INT32 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[3].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[3].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
+    tt_want_uint_op(iodev->info->mode_info[3].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[4].num_values, ==, 2);
     tt_want_uint_op(iodev->info->mode_info[4].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
@@ -1020,16 +1020,16 @@ static PT_THREAD(test_technic_xl_motor(struct pt *pt)) {
     tt_want_uint_op(iodev->mode, ==, 0);
 
     tt_want_uint_op(iodev->info->mode_info[0].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[0].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[1].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[1].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8);
+    tt_want_uint_op(iodev->info->mode_info[1].data_type, ==, PBIO_IODEV_DATA_TYPE_INT8 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[2].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[2].data_type, ==, PBIO_IODEV_DATA_TYPE_INT32);
+    tt_want_uint_op(iodev->info->mode_info[2].data_type, ==, PBIO_IODEV_DATA_TYPE_INT32 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[3].num_values, ==, 1);
-    tt_want_uint_op(iodev->info->mode_info[3].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
+    tt_want_uint_op(iodev->info->mode_info[3].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16 | PBIO_IODEV_DATA_TYPE_WRITABLE);
 
     tt_want_uint_op(iodev->info->mode_info[4].num_values, ==, 2);
     tt_want_uint_op(iodev->info->mode_info[4].data_type, ==, PBIO_IODEV_DATA_TYPE_INT16);
diff --git a/pybricks/util_pb/pb_device_stm32.c b/pybricks/util_pb/pb_device_stm32.c
index 572a5b39b..72676f7d6 100644
--- a/pybricks/util_pb/pb_device_stm32.c
+++ b/pybricks/util_pb/pb_device_stm32.c
@@ -115,7 +115,7 @@ void pb_device_get_values(pb_device_t *pbdev, uint8_t mode, int32_t *values) {
     }
 
     for (uint8_t i = 0; i < len; i++) {
-        switch (type) {
+        switch (type & PBIO_IODEV_DATA_TYPE_MASK) {
             case PBIO_IODEV_DATA_TYPE_INT8:
                 values[i] = *((int8_t *)(data + i * 1));
                 break;
@@ -153,7 +153,7 @@ void pb_device_set_values(pb_device_t *pbdev, uint8_t mode, int32_t *values, uin
     }
 
     for (uint8_t i = 0; i < len; i++) {
-        switch (type) {
+        switch (type & PBIO_IODEV_DATA_TYPE_MASK) {
             case PBIO_IODEV_DATA_TYPE_INT8:
                 *(int8_t *)(data + i) = values[i];
                 break;