RS232 CAN bus Node
Application note 002: PC to CAN interface (see 6393)

6392 as RS232 to CAN bus interface

To switch the 6392 RS232 node to its CANBUS interface mode, CFG6000 or WIN6000 sends the following 19 characters:

• A carriage return (ASCII code 13) to terminate any previous line
• A string of 17 characters: =<>*CDSYS6390*<>=
• A carriage return to terminate the string

The string is send with 8 data, 2 stopbits and no parity (the 6392 ignores its parity while decoding this string).

Because the actual 6392 BAUDRATE is unknown, it is send by CFG6000/WIN6000 on every possible speed (300/600/1200/2400/4800/9600/19200/38400) until the 6392 returns the string (confirmation), using its actual BAUDRATE.

Character offset

As soon the 6390 or 6392 is switched into the interface mode the character offset system is active and must be used.
(Some operating systems or programming languages will not accept some character under 32  
Routine is C and Pascal can be down loaded, see the bottom of this page.
  

While sending CAN messages via the 6392 the actual codes send via the PC COM port can be lower than 32.
Some PC programs (like the GWBASIC or QBASIC internal interrupt routines) do not handle all of these codes correctly, so a protocol is used to prevent the occurrence of these codes.

1) at the beginning of each CAN message, OFFSET is set to zero.
2) get character to send.
3) if (character code + OFFSET) < 32 : send 1 and set OFFSET to 32
4) if (character code + OFFSET) > 255: send 2 and set OFFSET to 0
5) send character code + OFFSET
6) goto step 2 if any more character to send
7) send carriage return

An example sting

Original string; 244 50 10 50 30 242 40 30

With offsets: 244 50 01 (10+32) (50+32) (30+32) 02 242 40 30 

So the string to (or from) the 6392 will be longer than the CAN message.

As soon as CFG6000/WIN6000 (or another PC program) has switched the 6392 into its interface mode, 
a few special CDAL commands can be given (CDAL using CAN identifier 2034), 
none of these commands will get a message response from the 6392. The commands are:

RS232 speed

 

CAN Header	Byte 1	Byte 2 (lsb)	Byte 3(msb)
FEh 43h	01h	2Ch	01h	(300bps)
		58h	02h	(600bps)
		B0h	04h	(1200bps)
		60h	09h	(2400bps)
		C0h	12h	(4800bps)
		80h	25h	(9600bps)
		00h	4Bh	(19200bps)
		00h	96h	(38400bps)

 

CAN bus speed

 

CAN Header	Byte 1	Byte 2 (lsb)	Byte 3(msb)
FEh 43h	03h	OAh	00h	(10Kbps)
		14h	00h	(20Kbps)
		32h	00h	(50Kbps)
		7Dh	00h	(125Kbps)
		FAh	00h	(250Kbps)
		F4h	01h	(500Kbps)
		E8h	03h	(1000Kbps)

The typical way to establish a connection to the CAN BUS via the 6392 is:

• set switch string (=<>*CDSYS6390*<>=) on all RS232 BAUDRATES until 6392 sends the same string back
• send RS232 BAUDRATE command (command 1) to switch 6392 to another speed.
  (don't forget to change the PC-COM speed as well)
  • An other RS232 baudrate can be set as default only when this device is connected as Node to the CAN bus,
    configure with the free available WIN6000 program.
• send CANBUS BAUDRATE command (command 3) to switch 6392 to used bus speed. (can be omitted if 6392 default speed is the speed in use)
  • An other CAN baudrate can be set as default only when this device is connected as Node to the CAN bus, 
    configure with the WIN6000 program.

C routines

We at CD Systems write already a few C routines for CANopen communication 
(including the character offset system) for the 6390/9392 RS232 to CAN interface.

Canoappl.C (p) contains CANopen routines  and make use of 

can_6390.C (p) for communication thru the 6390 device.

And for Pascal:

Canoappl,pas (p)

(p) protected part of our Internet site, files available for 6390/6392 users.  

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