Introduce an optional startOfSlaveFrameChar for Modus ASCII (#431)

* Option for slave frame delimiter * Typo in README * Fixed eslint errors * Eslint fix 2 * Eslint fix 3 * Esliont fix 4 * Eslint fix 5 * Eslint fix 6 * optional slave frame delimiter fixed * fixed typo
yaacov · Oct 26, 2021 · 691fcd1 · 691fcd1
1 parent 3acdb3b
commit 691fcd1
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diff --git a/README.md b/README.md
@@ -282,6 +282,40 @@ serverTCP.on("socketError", function(err){
     console.error(err);
 });
 ```
+----
+###### Read and Write Modbus ASCII
+``` javascript
+// create an empty modbus client
+var Modbus = require("modbus-serial");
+var client = new Modbus();
+
+// open connection to a serial port
+client.connectAsciiSerial(
+    "/dev/ttyUSB0", 
+    {
+        baudRate: 9600,
+        startOfSlaveFrameChar: 0x3A  // optional: slave frame delimiter
+    }, 
+    write);
+
+function write() {
+    client.setID(1);
+
+    // write the values 0, 0xffff to registers starting at address 5
+    // on device number 1.
+    client.writeRegisters(5, [0 , 0xffff])
+        .then(read);
+}
+
+function read() {
+    // read the 2 registers starting at address 5
+    // on device number 1.
+    client.readHoldingRegisters(5, 2)
+        .then(console.log);
+}
+```
+----
+
 
 to get more see [Examples](https://github.com/yaacov/node-modbus-serial/wiki)
 

diff --git a/ports/asciiport.js b/ports/asciiport.js
@@ -1,4 +1,6 @@
 "use strict";
+/* eslint-disable no-ternary */
+
 var util = require("util");
 var events = require("events");
 var EventEmitter = events.EventEmitter || events;
@@ -108,6 +110,12 @@ var AsciiPort = function(path, options) {
     // options
     options = options || {};
 
+    // select char for start of slave frame (usually :)
+    this._startOfSlaveFrameChar =
+        (options.startOfSlaveFrameChar === undefined)
+            ? 0x3A
+            : options.startOfSlaveFrameChar;
+
     // disable auto open, as we handle the open
     options.autoOpen = false;
 
@@ -130,7 +138,7 @@ var AsciiPort = function(path, options) {
         modbusSerialDebug(JSON.stringify({ action: "receive serial ascii port strings", data: data, buffer: modbus._buffer }));
 
         // check buffer for start delimiter
-        var sdIndex = modbus._buffer.indexOf(0x3E); // ascii for '>', as this indicates slave replies
+        var sdIndex = modbus._buffer.indexOf(modbus._startOfSlaveFrameChar);
         if(sdIndex === -1) {
             // if not there, reset the buffer and return
             modbus._buffer = Buffer.from("");

diff --git a/test/ports/asciiport.test.js b/test/ports/asciiport.test.js
@@ -18,7 +18,10 @@ describe("Modbus Ascii port", function() {
         mockery.enable({ warnOnReplace: false, useCleanCache: true, warnOnUnregistered: false });
         mockery.registerMock("serialport", mock);
         var AsciiPort = require("./../../ports/asciiport");
-        port = new AsciiPort("/dev/null", {});
+        port = new AsciiPort(
+            "/dev/null",
+            { startOfSlaveFrameChar: 0x3E }  // optional slave frame char ('>')
+        );
     });
 
     after(function() {
@@ -60,7 +63,7 @@ describe("Modbus Ascii port", function() {
             port.open(function() {
                 port.write(Buffer.from("1103006B00037687", "hex"));
                 setTimeout(function() {
-                    port._client.receive(Buffer.from(">", "ascii"));
+                    port._client.receive(Buffer.from(">", "ascii"));  // changed slave frame char
                     port._client.receive(Buffer.from("11", "ascii"));
                     port._client.receive(Buffer.from("03", "ascii"));
                     port._client.receive(Buffer.from("06", "ascii"));
@@ -76,7 +79,7 @@ describe("Modbus Ascii port", function() {
             });
         });
 
-        it("should return a valid Modbus RTU exception", function(done) {
+        it("should return a valid Modbus ASCII exception", function(done) {
             port.once("data", function(data) {
                 expect(data.toString("hex")).to.equal("1183044136");
                 done();
@@ -112,7 +115,7 @@ describe("Modbus Ascii port", function() {
             });
         });
 
-        it("Illegal start chars, should synchronize to valid Modbus RTU message", function(done) {
+        it("Illegal start chars, should synchronize to valid Modbus ASCII message", function(done) {
             port.once("data", function(data) {
                 expect(data.toString("hex")).to.equal("110306ae415652434049ad");
                 done();
@@ -140,7 +143,7 @@ describe("Modbus Ascii port", function() {
             });
         });
 
-        it("Illegal end chars, should return a valid Modbus RTU message", function(done) {
+        it("Illegal end chars, should return a valid Modbus ASCII message", function(done) {
             port.once("data", function(data) {
                 expect(data.toString("hex")).to.equal("110306ae415652434049ad");
                 done();
@@ -168,7 +171,7 @@ describe("Modbus Ascii port", function() {
             });
         });
 
-        it("should return a valid Modbus RTU message on illegal chars", function(done) {
+        it("should return a valid Modbus ASCII message on illegal chars", function(done) {
             port.once("data", function(data) {
                 expect(data.toString("hex")).to.equal("110306ae415652434049ad");
                 done();
@@ -194,7 +197,7 @@ describe("Modbus Ascii port", function() {
     });
 
     describe("#write", function() {
-        it("should write a valid RTU message to the port", function() {
+        it("should write a valid Modbus ASCII message to the port", function() {
             port.write(Buffer.from("1103006B00037687", "hex"));
             expect(port._client._data.toString("ascii")).to.equal(":1103006B00037E\r\n");
         });