MAX233 question

Scott M

I know, only vaguely related to BS/2s, but I figure folk here must have experience with MAX232 and MAX233 chips.

I'm trying to use a MAX233 (a 232 different pinout and the caps onboard) to bridge a stamp and a stereo component. For a simple test, I've tried just using the MAX as a loopback to a PC: I have the 5v output tied to the 5v input, and the RS-232 transmit and receive pins going from a PC to the chip. When I hit a character in hyperterminal, it should be immediately echoed back. But I get nothing.

Here's the pin layout. Am I missing something very obvious?

MAX pin 2 -> MAX pin 3 (send TTL output to input)

MAX pin 4 -> RS232 pin 3 (center bottom row, Tx)

MAX pin 5 -> RS232 pin 2 (Rx)

MAX pin 6 -> ground

MAX pin 7 -> +5v

MAX pin 9 -> ground

RS232 pin 5 -> ground

RS232 pin 7 -> RS232 pin 8 (standard stamp detect hack)

In Hyperterminal I've tried 2400 baud and·9600 baud, and Hardware and None for flow control.

I'm going mad - anyone have any suggestions? This wasn't supposed to be the hard part.
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upand_at_them

First, create a loopback plug to make sure the problem isn't your computer.
For a regular RS-232 DB9:

Connect pin 2 to pin 3.
Connect pin 1 to pin 4 to pin 6.
Connect pin 7 to pin 8.

Then, when you type anything in your terminal program is should be echoed back.

Mike

steve_b

Don't forget your DB9 pin5...it's gnd!·

uhm....not sure what you mean by tying the 5V input to the 5V output...do you mean the ttl output goes to the ttl input?

You're pinouts look right....BUT, I'm terrible with anything 50/50.· So, I'm always getting TX and RX mixed up on my rs232 connector.· So, change them around.

The baud rate won't matter, since you're sending at the rate you're to receive.

Now you don't need the caps on the 233 but you do need to short pins 11&15 and 16&10 and 12&17 and 6&9. (it's all in the datasheet)

I'd first try swapping my Rx and Tx!

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·

Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

upand_at_them

And looking at the datasheet you need to make other self connections on the MAX233:

Pin 12 to Pin 17.
Pin 11 to Pin 15.
Pin 10 to Pin 16.

These are pin numbers for the DIP package.

Mike

Scott M

Yup... I missed the other connections. I saw "Do not make connections to these pins" near some pins and assumed it belonged to all of them in that group. *mutter* Why doesn't the chip make these connections internally, if they are necessary?

Anyway, it works now, thanks everyone. Bizarre, Arcane Home Automation is now within my grasp. Bwah haha ha ha ha...