On the 18st Dec 2011 I´ve posted a question regarding MAX3221CUE transmission problem at avrfreaks forum. You can view my post here. I finally managed to solve the transmission problem & decided to share it. Just in case someone in the future bump into the same problem as i experienced, this post might be helpful.
Let me explain briefly what my problem was:
I was trying to transmit a character from microcontroller (atmega88) to Hyper Terminal Program on PC. When measured with oscilloscope, there´s a signal at T1IN pin but none at T1out pin. But when atmega88 is receiving a character from PC there´s no problem at all. Hmmm my MAX3221CUE chip is not functioning properly or might be defective, i suspected. This problem has bothered me for the past few days.
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| MAX3221CUE pin allocation |
I was about to order a new chip, assuming that mine was faulty. Apparently not. I just realized that the FORCEOFF & VCC pin of MAX3221 were not actually connected to each other. Both pins must be connected to one another for the transmitter to work properly. Otherwise the transmitter is in shutdown mode. At first sight all pins seem to be connected accordingly on the schematic. But when I clicked at the wire between VCC & FORCEOFF pin, the wire is not completely highlighted (light green). Troublemaker spotted!
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| Schematic & Board layout before Transmission Problem solved |
So I redrew the line between both pins & this time I make sure that the line is completely highlighted as shown below when selected.
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/sweat
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| MAX3221CUE on PCB |
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