Hello all, just wanted to see if anyone else has experienced this or has any suggestions... I ordered some free samples of the MAX233 chip to build myself a TTL-to-RS232 serial converter. (The MAX233 is the same as a MAX232 but with internal capacitors).
After constructing the cable and triple-checking all my connections, when I try to send data over the line, the computer is receiving inverted bits. I got out the voltmeter and discovered I could not measure ANY negative voltages coming out of the MAX233, not even on the V- pin.
- I am providing the chip with regulated +5V
- I am connecting the TTL end to an AVR mega48 (actually a Baby Orangutan controller)
- I have checked and re-checked all my connections, and as far as I can tell, everything is hooked up as specified in the MAX233 datasheet
- I'm using a 1.0 uF electrolytic capacitor between Vcc and GND (as specified in the datasheet)
- Pins 6 and 9 (both GND) are tied together
- I'm using T1 in/out, and R1 in/out, T2 and R2 are left floating (should they be tied high or low?)
- I have tried the connection with two separate MAX233 chips, they both provide the same results
The only thing I can imagine is that I ordered the wrong variation of the part...? The chip is labelled MAX233CPP, and I'm afraid I know nothing about IC suffixes (what does the CPP mean?).
Any advice or assistance would be appreciated.
In the meantime, I went ahead and ordered a properly-manufactured TTL-to-RS232 conversion cable from RobotShop.ca, but I would like to solve this problem, if only as a learning experience.
Attached is a quick-and-dirty diagram of my connections. Can anyone see anything obviously wrong with this? Even if my connections are
incorrect, I still can't figure out why the chip doesn't appear to be providing any negative voltages.