Differences

This shows you the differences between two versions of the page.

--- modbus [2011/11/06 21:59]
jap
+++ modbus [2011/11/07 16:40]
jap
@@ Line 35: / Line 35: @@
 Here is a simple test software that reads given number of register values from modbus slave and prints them to ''stdout''. This application is made only to study libmodbus and test modbus interface.
-Build the code with following command:
+Build the code with the command below. In Debian, at least following packages are needed: ''build-essential, pkg-config''.
-  cc `pkg-config --cflags --libs libmodbus` mbtest.c -o mbtest
+  $ cc `pkg-config --cflags --libs libmodbus` mbtest.c -o mbtest
 Source code of mbtest.c:
-  #include <stdio.h>
+<file>
-  #include <modbus.h>
+#include <stdio.h>
+#include <modbus.h>
-  #define MB_BITRATE 19200
-  #define MB_DATABITS 8
+#define MB_BITRATE 19200
-  #define MB_STOPBITS 1
+#define MB_DATABITS 8
-  #define MB_PARITY 'N'
+#define MB_STOPBITS 1
-  #define MB_SLAVE_ADDRESS 1
+#define MB_PARITY 'N'
+#define MB_SLAVE_ADDRESS 1
-  #define MB_REG_BASE 0
-  #define MB_REG_COUNT 16
+#define MB_REG_BASE 6
+#define MB_REG_COUNT 4
-  int main ( int argc, char* argv[] )
-  {
+int main ( int argc, char* argv[] )
-    modbus_t *ctx;
+{
-    uint16_t tab_reg[32];
+  modbus_t *ctx;
-    int n, i;
+  uint16_t tab_reg[32];
+  int n, i;
-    if ( argc != 2 )
+  int errno = 0;
+  if ( argc != 2 )
     {
       fprintf(stderr, "Syntax: %s serial_device\n", argv[0]);
       return -1;
     }
-    ctx = modbus_new_rtu(argv[1],
+  ctx = modbus_new_rtu(argv[1],
 		       MB_BITRATE,
 		       MB_PARITY,
 		       MB_DATABITS,
 		       MB_STOPBITS);
-    if (ctx == NULL)
+  if (ctx == NULL) {
-    {
     fprintf(stderr,
 	    "Unable to create the libmodbus context on serial port %s\n",
 	    argv[1]);
-    return -1
+    return -1;
-    }
+  }
-    if ( modbus_set_slave(ctx, MB_SLAVE_ADDRESS) )
+  if ( modbus_set_slave(ctx, MB_SLAVE_ADDRESS) )
     {
       fprintf(stderr,
 	      "Failed to set modbus slave address\n");
+      errno = -1;
       goto fail;
     }
-    if ( modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485) )
+  if ( modbus_connect(ctx))
-    {
-      fprintf(stderr,
-	      "Failed to set modbus mode\n");
-      goto fail;
-    }
-    if ( modbus_connect(ctx))
     {
       fprintf(stderr,
 	      "Unable to connect to modbus server");
+      errno = -1;
       goto fail;
     }
-    n = modbus_read_registers(ctx, MB_REG_BASE, MB_REG_COUNT, tab_reg);
+  n = modbus_read_registers(ctx,
-    if ( n <= 0 )
+			    MB_REG_BASE,
+			    MB_REG_COUNT,
+			    tab_reg+MB_REG_BASE);
+  if ( n <= 0 )
     {
       fprintf(stderr,
 	      "Unable to read modbus registers\n");
+      errno = -1;
       goto fail;
     }
-    for ( i=MB_REG_BASE; i<MB_REG_BASE+n; i++ )
+  for ( i=MB_REG_BASE; i<MB_REG_BASE+n; i++ )
     {
       printf ( "[%d]: %d\n", i, tab_reg[i]);
     }
-  fail:
+ fail:
-    modbus_close(ctx);
+  modbus_close(ctx);
-    modbus_free(ctx);
+  modbus_free(ctx);
-  return 0;
+  return errno;
-  }
+}
+</file>