diff --git a/examples/modbus/rtu_master.py b/examples/modbus/rtu_master.py
index 50e157580..9bd14166e 100644
--- a/examples/modbus/rtu_master.py
+++ b/examples/modbus/rtu_master.py
@@ -1,21 +1,24 @@
 import modbus
 
-mb_tcp = modbus.ModBusRTU(128, 128)
-mb_tcp.setSlave(1)
+mb = modbus.ModBusRTU(128, 128)
+mb.setSlave(1)
 
-send_buff = mb_tcp.serializeReadRegisters(0, 10)
+send_buff = mb.serializeReadRegisters(0, 10)
 print(send_buff)
 
-host_regists = mb_tcp.deserializeReadRegisters(
+host_regists = mb.deserializeReadRegisters(
     b'\x01\x03\x14\x00\x00\x00\x00\x04\xD2\x00\x00\x00\x00\x00\x7B\x00\x00\x00\x00\x00\x00\x00\x00\xE5\x0B'
 )
 print(host_regists)
 
 
-mb_tcp.serializeReadInputRegisters(0, 2)
+mb.serializeReadInputRegisters(0, 2)
 
-mb_tcp.deserializeReadInputRegisters(b'\x01\x04\x04\x00\x00\x08\xE6\x7D\xCE')
+mb.deserializeReadInputRegisters(b'\x01\x04\x04\x00\x00\x08\xE6\x7D\xCE')
 
 
-send_buff = mb_tcp.serializeWriteRegister(0, 0x1234)
+send_buff = mb.serializeWriteRegister(0, 0x1234)
+print(send_buff)
+
+send_buff = mb.serializeWriteBits(0, [1, 1, 1, 0, 1, 0, 1, 0])
 print(send_buff)
diff --git a/package/modbus/modbus.py b/package/modbus/modbus.py
index c0f020e7c..69b6cf8d7 100644
--- a/package/modbus/modbus.py
+++ b/package/modbus/modbus.py
@@ -4,7 +4,7 @@ import _modbus
 class ModBus(_modbus._ModBus):
 
     def serializeWriteBits(self, addr: int, src: list) -> bytes:
-        lenth = super().serializeWriteBits(addr, len(list), bytes(src))
+        lenth = super().serializeWriteBits(addr, len(src), bytes(src))
         return self.sendBuff[0:lenth]
 
     def serializeWriteRegisters(self, addr: int, src: list) -> bytes:
diff --git a/port/linux/package/pikascript/modbus.py b/port/linux/package/pikascript/modbus.py
index c0f020e7c..69b6cf8d7 100644
--- a/port/linux/package/pikascript/modbus.py
+++ b/port/linux/package/pikascript/modbus.py
@@ -4,7 +4,7 @@ import _modbus
 class ModBus(_modbus._ModBus):
 
     def serializeWriteBits(self, addr: int, src: list) -> bytes:
-        lenth = super().serializeWriteBits(addr, len(list), bytes(src))
+        lenth = super().serializeWriteBits(addr, len(src), bytes(src))
         return self.sendBuff[0:lenth]
 
     def serializeWriteRegisters(self, addr: int, src: list) -> bytes:
diff --git a/test/module-test.cpp b/test/module-test.cpp
index 6ae489a69..d71d1f0c1 100644
--- a/test/module-test.cpp
+++ b/test/module-test.cpp
@@ -396,15 +396,17 @@ TEST(modbus, rtu_master) {
     pikaVM_runSingleFile(pikaMain, "test/python/modbus/rtu_master.py");
     /* collect */
     /* assert */
-    EXPECT_STREQ(log_buff[5], "BEGIN\r\n");
-    EXPECT_STREQ(log_buff[4],
+    EXPECT_STREQ(log_buff[6], "BEGIN\r\n");
+    EXPECT_STREQ(log_buff[5],
                  "b'\\x01\\x03\\x00\\x00\\x00\\x0a\\xc5\\xcd'\r\n");
-    EXPECT_STREQ(log_buff[3], "[0, 0, 1234, 0, 0, 123, 0, 0, 0, 0]\r\n");
-    EXPECT_STREQ(log_buff[2],
+    EXPECT_STREQ(log_buff[4], "[0, 0, 1234, 0, 0, 123, 0, 0, 0, 0]\r\n");
+    EXPECT_STREQ(log_buff[3],
                  "b'\\x01\\x04\\x00\\x00\\x00\\x02\\x71\\xcb'\r\n");
-    EXPECT_STREQ(log_buff[1], "[0, 2278]\r\n");
-    EXPECT_STREQ(log_buff[0],
+    EXPECT_STREQ(log_buff[2], "[0, 2278]\r\n");
+    EXPECT_STREQ(log_buff[1],
                  "b'\\x01\\x06\\x00\\x00\\x12\\x34\\x84\\xbd'\r\n");
+    EXPECT_STREQ(log_buff[0],
+                 "b'\\x01\\x0f\\x00\\x00\\x00\\x08\\x01\\x57\\xbf\\x6b'\r\n");
     /* deinit */
     obj_deinit(pikaMain);
     EXPECT_EQ(pikaMemNow(), 0);
diff --git a/test/python/modbus/rtu_master.py b/test/python/modbus/rtu_master.py
index 50e157580..9bd14166e 100644
--- a/test/python/modbus/rtu_master.py
+++ b/test/python/modbus/rtu_master.py
@@ -1,21 +1,24 @@
 import modbus
 
-mb_tcp = modbus.ModBusRTU(128, 128)
-mb_tcp.setSlave(1)
+mb = modbus.ModBusRTU(128, 128)
+mb.setSlave(1)
 
-send_buff = mb_tcp.serializeReadRegisters(0, 10)
+send_buff = mb.serializeReadRegisters(0, 10)
 print(send_buff)
 
-host_regists = mb_tcp.deserializeReadRegisters(
+host_regists = mb.deserializeReadRegisters(
     b'\x01\x03\x14\x00\x00\x00\x00\x04\xD2\x00\x00\x00\x00\x00\x7B\x00\x00\x00\x00\x00\x00\x00\x00\xE5\x0B'
 )
 print(host_regists)
 
 
-mb_tcp.serializeReadInputRegisters(0, 2)
+mb.serializeReadInputRegisters(0, 2)
 
-mb_tcp.deserializeReadInputRegisters(b'\x01\x04\x04\x00\x00\x08\xE6\x7D\xCE')
+mb.deserializeReadInputRegisters(b'\x01\x04\x04\x00\x00\x08\xE6\x7D\xCE')
 
 
-send_buff = mb_tcp.serializeWriteRegister(0, 0x1234)
+send_buff = mb.serializeWriteRegister(0, 0x1234)
+print(send_buff)
+
+send_buff = mb.serializeWriteBits(0, [1, 1, 1, 0, 1, 0, 1, 0])
 print(send_buff)