diff --git a/deno.json b/deno.json
index abdb72e..d9a27b3 100644
--- a/deno.json
+++ b/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@joyautomation/tentacle",
-  "version": "0.0.36",
+  "version": "0.0.43",
   "description": "Tentacle is a modern soft PLC",
   "author": "Joy Automation",
   "license": "Apache-2.0",
diff --git a/modbus/client.ts b/modbus/client.ts
index 828616a..07cfeff 100644
--- a/modbus/client.ts
+++ b/modbus/client.ts
@@ -337,6 +337,25 @@ function readModbusFormatValue(
   throw new Error(`Unsupported format: ${format}`);
 }
 
+function writeModbusFormatValue(value: number, format: string, modbus: Modbus): number[] {
+  const buffer = new ArrayBuffer(4)
+  const view = new DataView(buffer)
+  const data: number[] = []
+  if (format === `FLOAT`) {
+    view.setFloat32(0, value)
+    data.push(view.getUint16(modbus.reverseWords ? 2 : 0, modbus.reverseBits))
+    data.push(view.getUint16(modbus.reverseWords ? 0 : 2, modbus.reverseBits))
+  } else if (format === `INT32`) {
+    view.setInt32(0, value)
+    data.push(view.getUint16(modbus.reverseWords ? 2 : 0, modbus.reverseBits))
+    data.push(view.getUint16(modbus.reverseWords ? 0 : 2, modbus.reverseBits))
+  } else if (format === `INT16`) {
+    view.setInt16(0, value)
+    data.push(view.getUint16(0, modbus.reverseBits))
+  }
+  return data
+}
+
 export type ModbusError = {
   name: string;
   message: string;
@@ -431,6 +450,7 @@ export type ModbusWriteFunctions = {
 export async function writeModbus(
   register: number,
   registerType: "HOLDING_REGISTER" | "COIL",
+  format: ModbusFormat,
   modbus: Modbus,
   value: number | boolean,
 ): Promise<Result<void>> {
@@ -444,6 +464,7 @@ export async function writeModbus(
     );
   }
 
+  modbus.client.writeRegisters
   const functionMap: ModbusWriteFunctions = {
     HOLDING_REGISTER: modbus.client.writeRegisters.bind(modbus.client),
     COIL: modbus.client.writeCoils.bind(modbus.client),
@@ -451,7 +472,7 @@ export async function writeModbus(
 
   const result = await Promise.race([
     // @ts-ignore fix this type problem later
-    functionMap[registerType](register, [value])
+    functionMap[registerType](register, writeModbusFormatValue(value, format, modbus))
       .then(() => createSuccess(undefined))
       .catch((error) => createFail(error)),
     timeoutPromise(3000),
diff --git a/plc/runtime.ts b/plc/runtime.ts
index dbbdb30..8972081 100644
--- a/plc/runtime.ts
+++ b/plc/runtime.ts
@@ -365,15 +365,19 @@ export function startSourceIntervals<
                     const writeResult = await writeModbus(
                       variable.source.register,
                       variable.source.registerType,
+                      variable.source.format,
                       source.client,
                       //@ts-ignore fix type
-                      currentVariable.value
+                      variable.source.onSend
+                      //@ts-expect-error TODO: fix type later
+                        ? variable.source.onSend(currentVariable.value)
+                        : currentVariable.value
                     );
                     if (isFail(writeResult)) {
                       log.warn(
-                        `Failed to write to modbus ${source.id} - ${variableId}: ${writeResult.error}`
+                        `Failed to write to modbus ${source.id} - ${variableId}: ${JSON.stringify(writeResult.message)}`
                       );
-                      updateRuntimeError(plc, variableId, writeResult.error);
+                      updateRuntimeError(plc, variableId, writeResult.message || "Unknown error");
                     }
                     clearRuntimeError(plc, variableId);
                   }
diff --git a/synapse.ts b/synapse.ts
index 0cd12fa..a87c73a 100644
--- a/synapse.ts
+++ b/synapse.ts
@@ -22,6 +22,8 @@ import { getModbusStateString } from "./modbus/client.ts";
 import type { PlcMqtts } from "./types/mqtt.ts";
 import { updateRuntimeValue } from "./plc/runtime.ts";
 import type { Buffer } from "node:buffer";
+import { logs } from "./log.ts";
+const log = logs.main;
 
 export const variableTypeToSparkplugType = (datatype: string): TypeStr => {
   switch (datatype) {
@@ -195,10 +197,14 @@ export function createPlcMqtt<
                 for (const [variableId, variable] of Object.entries(
                   variables
                 )) {
-                  const value = variable.source.onResponse
-                    ? variable.source.onResponse(message)
-                    : message;
-                  updateRuntimeValue(plc, variableId, value);
+                  try {
+                    const value = variable.source.onResponse
+                      ? variable.source.onResponse(message)
+                      : message;
+                    updateRuntimeValue(plc, variableId, value);
+                  } catch (error) {
+                    log.warn(`Error updating variable ${variableId}: ${error}`);
+                  }
                 }
               },
             ];