BS2 to PLC via RS485

[anthr4x]

Hello, I'm new to the world of Basic Stamps and am having some trouble getting my BS2 to communicate with my PLC over RS485.

When I send this:
SEROUT 6,baud, [DEC 48,DEC 49,DEC 50,DEC 51,DEC 52,DEC 53,DEC 54,DEC 55]

My PLC is receiving:
83 83 d0 b0 90 70 50

If I send:
SEROUT 6,baud, [HEX 48,HEX 49,HEX 50,HEX 51,HEX 52,HEX 53,HEX 54,HEX 55]

I receive this:
99 f0 83 06 2e

If I send:
SEROUT 6,baud, [48, 49, 50, 51, 52, 53, 54, 55]

I receive randomly:
f0 46 c6 19 93
a3 c6 19 93
46 c6 19 93

I am using this http://www.sparkfun.com/commerce/product_info.php?products_id=9083
It uses a MAX485 CSA chip.

Can anyone make sense of what I'm receiving?

[Mike Green]

1) Are you sure you have the proper Baud constant in the SERIN and SEROUT statements for the requirements of your PLC?

2) The MAX485 is a half duplex RS485 driver. The SparkFun documentation link gives no information about how the direction of the MAX485 is controlled. How do you have things hooked up?

[Phil Pilgrim (PhiPi)]

In addition to Mike's comments, if you're sure you have the right baud rate, you may have TX+ and TX- reversed. BTW, the values you're sending are ASCII for "01234567". If that's what you intend to send, your third example is the correct one, or you could just do: SEROUT 6, baud, ["01234567"]

-Phil

[allanlane5]

You also need to attach a ground wire between the BS2 and the RS485 chip. It's also possible you need to add the 'invert' value to the baud-mode select value.

Edit: What PhiPi says is very true.

Post Edited (allanlane5) : 4/6/2010 4:47:22 PM GMT

[Phil Pilgrim (PhiPi)]

allanlane5 said...
It's also possible you need to add the 'invert' value to the baud-mode select value.

This would be equivalent to reversing TX+ and TX-, as I suggested above.

-Phil

[anthr4x]

I can send with my BS2 now and my PLC is receiving the right values. My problem was it needed to be inverted. I'm using $4054 for my baud constant now. Now I need to get my BS2 to receive. Mike, I need to controll the direction of the MAX485?


Mike Green said...

2) The MAX485 is a half duplex RS485 driver. The SparkFun documentation link gives no information about how the direction of the MAX485 is controlled. How do you have things hooked up?