Diff: SimpleModbusSlave.h

Revision:

0:7c5265097fd2

Child:

1:85e226914fb7

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SimpleModbusSlave.h	Tue Oct 10 12:22:31 2017 +0000
@@ -0,0 +1,89 @@
+#ifndef SIMPLE_MODBUS_SLAVE_H
+#define SIMPLE_MODBUS_SLAVE_H
+
+/*
+ SimpleModbusSlave allows you to communicate
+ to any slave using the Modbus RTU protocol.
+ 
+ The crc calculation is based on the work published 
+ by jpmzometa at 
+ http://sites.google.com/site/jpmzometa/arduino-mbrt
+ 
+ By Juan Bester : bester.juan@gmail.com
+ 
+ The functions implemented are functions 3 and 16.
+ read holding registers and preset multiple registers
+ of the Modbus RTU Protocol, to be used over the Arduino serial connection.
+ 
+ This implementation DOES NOT fully comply with the Modbus specifications.
+ 
+ Specifically the frame time out have not been implemented according
+ to Modbus standards. The code does however combine the check for
+ inter character time out and frame time out by incorporating a maximum
+ time out allowable when reading from the message stream.
+ 
+ These library of functions are designed to enable a program send and
+ receive data from a device that communicates using the Modbus protocol.
+ 
+ SimpleModbusSlave implements an unsigned int return value on a call to modbus_update().
+ This value is the total error count since the slave started. It's useful for fault finding.
+ 
+ This code is for a Modbus slave implementing functions 3 and 16
+ function 3: Reads the binary contents of holding registers (4X references)
+ function 16: Presets values into a sequence of holding registers (4X references)
+ 
+ All the functions share the same register array.
+ 
+ Exception responses:
+ 1 ILLEGAL FUNCTION
+ 2 ILLEGAL DATA ADDRESS
+ 3 ILLEGAL DATA VALUE
+ 
+ Note:  
+ The Arduino serial ring buffer is 128 bytes or 64 registers.
+ Most of the time you will connect the arduino to a master via serial
+ using a MAX485 or similar.
+ 
+ In a function 3 request the master will attempt to read from your
+ slave and since 5 bytes is already used for ID, FUNCTION, NO OF BYTES
+ and two BYTES CRC the master can only request 122 bytes or 61 registers.
+ 
+ In a function 16 request the master will attempt to write to your 
+ slave and since a 9 bytes is already used for ID, FUNCTION, ADDRESS, 
+ NO OF REGISTERS, NO OF BYTES and two BYTES CRC the master can only write
+ 118 bytes or 59 registers.
+ 
+ Using the FTDI converter ic the maximum bytes you can send is limited 
+ to its internal buffer which is 60 bytes or 30 unsigned int registers. 
+ 
+ Thus:
+ 
+ In a function 3 request the master will attempt to read from your
+ slave and since 5 bytes is already used for ID, FUNCTION, NO OF BYTES
+ and two BYTES CRC the master can only request 54 bytes or 27 registers.
+ 
+ In a function 16 request the master will attempt to write to your 
+ slave and since a 9 bytes is already used for ID, FUNCTION, ADDRESS, 
+ NO OF REGISTERS, NO OF BYTES and two BYTES CRC the master can only write
+ 50 bytes or 25 registers.
+  
+ Since it is assumed that you will mostly use the Arduino to connect to a 
+ master without using a USB to Serial converter the internal buffer is set
+ the same as the Arduino Serial ring buffer which is 128 bytes.
+ 
+ The functions included here have been derived from the 
+ Modbus Specifications and Implementation Guides
+ 
+ http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf
+ http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf
+ http://www.modbus.org/docs/PI_MBUS_300.pdf
+*/
+
+
+
+// function definitions
+void modbus_configure(long baud, char _slaveID, char _TxEnablePin, unsigned int _holdingRegsSize, unsigned char _lowLatency);
+unsigned int modbus_update(unsigned int *holdingRegs);
+ 
+
+#endif