diff --git a/docs/library/machine.I2C.rst b/docs/library/machine.I2C.rst
index b3bfa68f075a2de4b89f50f5c8adc35b6913661a..f5820f103edfd5387b046a43ac67f00465aa5c5d 100644
--- a/docs/library/machine.I2C.rst
+++ b/docs/library/machine.I2C.rst
@@ -170,8 +170,7 @@ methods are convenience functions to communicate with such devices.
 
    Read `nbytes` from the slave specified by `addr` starting from the memory
    address specified by `memaddr`.
-   The argument `addrsize` specifies the address size in bits (on ESP8266
-   this argument is not recognised and the address size is always 8 bits).
+   The argument `addrsize` specifies the address size in bits.
    Returns a `bytes` object with the data read.
 
 .. method:: I2C.readfrom_mem_into(addr, memaddr, buf, \*, addrsize=8)
diff --git a/extmod/machine_i2c.c b/extmod/machine_i2c.c
index f7d238024526e873a5fe698b4f9f1897cc355631..d76e5eedd1bfe9798fba261626b88ee0a24a1ef5 100644
--- a/extmod/machine_i2c.c
+++ b/extmod/machine_i2c.c
@@ -128,24 +128,6 @@ STATIC int mp_hal_i2c_write_byte(machine_i2c_obj_t *self, uint8_t val) {
     return !ret;
 }
 
-STATIC void mp_hal_i2c_write(machine_i2c_obj_t *self, uint8_t addr, uint8_t *data, size_t len) {
-    mp_hal_i2c_start(self);
-    if (!mp_hal_i2c_write_byte(self, addr << 1)) {
-        goto er;
-    }
-    while (len--) {
-        if (!mp_hal_i2c_write_byte(self, *data++)) {
-            goto er;
-        }
-    }
-    mp_hal_i2c_stop(self);
-    return;
-
-er:
-    mp_hal_i2c_stop(self);
-    nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
-}
-
 STATIC int mp_hal_i2c_read_byte(machine_i2c_obj_t *self, uint8_t *val, int nack) {
     mp_hal_i2c_delay(self);
     mp_hal_i2c_scl_low(self);
@@ -172,33 +154,27 @@ STATIC int mp_hal_i2c_read_byte(machine_i2c_obj_t *self, uint8_t *val, int nack)
     return 1; // success
 }
 
-STATIC void mp_hal_i2c_read(machine_i2c_obj_t *self, uint8_t addr, uint8_t *data, size_t len) {
-    mp_hal_i2c_start(self);
-    if (!mp_hal_i2c_write_byte(self, (addr << 1) | 1)) {
-        goto er;
+// addr is the device address, memaddr is a memory address sent big-endian
+STATIC int mp_hal_i2c_write_addresses(machine_i2c_obj_t *self, uint8_t addr,
+        uint32_t memaddr, uint8_t addrsize) {
+    if (!mp_hal_i2c_write_byte(self, addr << 1)) {
+        return 0; // error
     }
-    while (len--) {
-        if (!mp_hal_i2c_read_byte(self, data++, len == 0)) {
-            goto er;
+    for (int16_t i = addrsize - 8; i >= 0; i -= 8) {
+        if (!mp_hal_i2c_write_byte(self, memaddr >> i)) {
+            return 0; // error
         }
     }
-    mp_hal_i2c_stop(self);
-    return;
-
-er:
-    mp_hal_i2c_stop(self);
-    nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
+    return 1; // success
 }
 
-STATIC void mp_hal_i2c_write_mem(machine_i2c_obj_t *self, uint8_t addr, uint16_t memaddr, const uint8_t *src, size_t len) {
+STATIC void mp_hal_i2c_write_mem(machine_i2c_obj_t *self, uint8_t addr,
+        uint32_t memaddr, uint8_t addrsize, const uint8_t *src, size_t len) {
     // start the I2C transaction
     mp_hal_i2c_start(self);
 
     // write the slave address and the memory address within the slave
-    if (!mp_hal_i2c_write_byte(self, addr << 1)) {
-        goto er;
-    }
-    if (!mp_hal_i2c_write_byte(self, memaddr)) {
+    if (!mp_hal_i2c_write_addresses(self, addr, memaddr, addrsize)) {
         goto er;
     }
 
@@ -218,20 +194,30 @@ er:
     nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
 }
 
-STATIC void mp_hal_i2c_read_mem(machine_i2c_obj_t *self, uint8_t addr, uint16_t memaddr, uint8_t *dest, size_t len) {
+STATIC void mp_hal_i2c_read_mem(machine_i2c_obj_t *self, uint8_t addr,
+        uint32_t memaddr, uint8_t addrsize, uint8_t *dest, size_t len) {
     // start the I2C transaction
     mp_hal_i2c_start(self);
 
-    // write the slave address and the memory address within the slave
-    if (!mp_hal_i2c_write_byte(self, addr << 1)) {
-        goto er;
+    if (addrsize) {
+        // write the slave address and the memory address within the slave
+        if (!mp_hal_i2c_write_addresses(self, addr, memaddr, addrsize)) {
+            goto er;
+        }
+
+        // i2c_read will do a repeated start, and then read the I2C memory
+        mp_hal_i2c_start(self);
     }
-    if (!mp_hal_i2c_write_byte(self, memaddr)) {
+
+    if (!mp_hal_i2c_write_byte(self, (addr << 1) | 1)) {
         goto er;
     }
-
-    // i2c_read will do a repeated start, and then read the I2C memory
-    mp_hal_i2c_read(self, addr, dest, len);
+    while (len--) {
+        if (!mp_hal_i2c_read_byte(self, dest++, len == 0)) {
+            goto er;
+        }
+    }
+    mp_hal_i2c_stop(self);
     return;
 
 er:
@@ -239,6 +225,14 @@ er:
     nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
 }
 
+STATIC void mp_hal_i2c_write(machine_i2c_obj_t *self, uint8_t addr, const uint8_t *src, size_t len) {
+    mp_hal_i2c_write_mem(self, addr, 0, 0, src, len);
+}
+
+STATIC void mp_hal_i2c_read(machine_i2c_obj_t *self, uint8_t addr, uint8_t *dest, size_t len) {
+    mp_hal_i2c_read_mem(self, addr, 0, 0, dest, len);
+}
+
 /******************************************************************************/
 // MicroPython bindings for I2C
 
@@ -367,68 +361,64 @@ STATIC mp_obj_t machine_i2c_writeto(mp_obj_t self_in, mp_obj_t addr_in, mp_obj_t
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(machine_i2c_writeto_obj, machine_i2c_writeto);
 
+STATIC const mp_arg_t machine_i2c_mem_allowed_args[] = {
+    { MP_QSTR_addr,    MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
+    { MP_QSTR_memaddr, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
+    { MP_QSTR_arg,     MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+    { MP_QSTR_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} },
+};
+
 STATIC mp_obj_t machine_i2c_readfrom_mem(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_addr, ARG_memaddr, ARG_n, ARG_addrsize };
-    static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_addr,    MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_memaddr, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_n,       MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        //{ MP_QSTR_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} }, TODO
-    };
     machine_i2c_obj_t *self = MP_OBJ_TO_PTR(pos_args[0]);
-    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
-    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+    mp_arg_val_t args[MP_ARRAY_SIZE(machine_i2c_mem_allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args,
+        MP_ARRAY_SIZE(machine_i2c_mem_allowed_args), machine_i2c_mem_allowed_args, args);
 
     // create the buffer to store data into
     vstr_t vstr;
-    vstr_init_len(&vstr, args[ARG_n].u_int);
+    vstr_init_len(&vstr, mp_obj_get_int(args[ARG_n].u_obj));
 
     // do the transfer
-    mp_hal_i2c_read_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int, (uint8_t*)vstr.buf, vstr.len);
+    mp_hal_i2c_read_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int,
+        args[ARG_addrsize].u_int, (uint8_t*)vstr.buf, vstr.len);
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(machine_i2c_readfrom_mem_obj, 1, machine_i2c_readfrom_mem);
 
+
 STATIC mp_obj_t machine_i2c_readfrom_mem_into(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_addr, ARG_memaddr, ARG_buf, ARG_addrsize };
-    static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_addr,    MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_memaddr, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_buf,     MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
-        //{ MP_QSTR_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} }, TODO
-    };
     machine_i2c_obj_t *self = MP_OBJ_TO_PTR(pos_args[0]);
-    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
-    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+    mp_arg_val_t args[MP_ARRAY_SIZE(machine_i2c_mem_allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args,
+        MP_ARRAY_SIZE(machine_i2c_mem_allowed_args), machine_i2c_mem_allowed_args, args);
 
     // get the buffer to store data into
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[ARG_buf].u_obj, &bufinfo, MP_BUFFER_WRITE);
 
     // do the transfer
-    mp_hal_i2c_read_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int, bufinfo.buf, bufinfo.len);
+    mp_hal_i2c_read_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int,
+        args[ARG_addrsize].u_int, bufinfo.buf, bufinfo.len);
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(machine_i2c_readfrom_mem_into_obj, 1, machine_i2c_readfrom_mem_into);
 
 STATIC mp_obj_t machine_i2c_writeto_mem(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_addr, ARG_memaddr, ARG_buf, ARG_addrsize };
-    static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_addr,    MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_memaddr, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_buf,     MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
-        //{ MP_QSTR_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} }, TODO
-    };
     machine_i2c_obj_t *self = MP_OBJ_TO_PTR(pos_args[0]);
-    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
-    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+    mp_arg_val_t args[MP_ARRAY_SIZE(machine_i2c_mem_allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args,
+        MP_ARRAY_SIZE(machine_i2c_mem_allowed_args), machine_i2c_mem_allowed_args, args);
 
     // get the buffer to write the data from
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[ARG_buf].u_obj, &bufinfo, MP_BUFFER_READ);
 
     // do the transfer
-    mp_hal_i2c_write_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int, bufinfo.buf, bufinfo.len);
+    mp_hal_i2c_write_mem(self, args[ARG_addr].u_int, args[ARG_memaddr].u_int,
+        args[ARG_addrsize].u_int, bufinfo.buf, bufinfo.len);
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(machine_i2c_writeto_mem_obj, 1, machine_i2c_writeto_mem);