MAX232 question

LearnerNM

Hello: I'm curious about the serial port adapter on the BOE board. Does it have a MAX232 chip? If not, is the MAX232 an adapter I will need to use instead of the port adapter on the board? Thanks.

Mike Green

No, it doesn't use a MAX232 chip. The Stamp has a couple of transistors and resistors on the substrate that allow it to communicate using RS232 voltages on the programming port (Sin/Sout). The BOE does have a couple of capacitors on DTR that make sure that the Atn pin gets a clean pulse when DTR is asserted (to reset the Stamp). The schematics are in the PBasic manual.

You can use the DB9 port for debugging and data as long as your application can tolerate a reset every time the serial port is opened/closed. If you want an RS232 connection to other I/O pins, you can either use a MAX232 or you can probably get by with a resistor or two as shown in the PBasic manual in the section on the SEROUT and SERIN statements.

LearnerNM

Thank you Mike.

Chris Savage

Hello,

You may also need a MAX232 on the I/O pins if the device you’re trying to communicate with requires handshaking signals since these are not available on the BOE programming port. Some devices also require RS-232 levels rather than the inverted TTL signals from that port when talking to DCE equipment. Take care.

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Chris Savage
Parallax Tech Support

LearnerNM

Thanks Chris. Next, is there any particular MAX232 more compatible with the STAMP than another? Suggestions?

Chris Savage

I think you’ll find the MAX232CPE to be the part number you want to search for. For the most part a MAX232 is a MAX232 although there are a few variants. I hope this helps. Take care.

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Chris Savage
Parallax Tech Support