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16f877a Max232 Db9

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Hello this forum has been very helpful in my graduation project.i would be very thankful if some one can show me the schematics of connecting a 16f877a max232 db9 to a pc.i would like to send text from the Pic to the computer using a port on a pic as inputs,Ex:if Portd.f1==1,send letter 'a' to pc.if portd.f2==1,send letter 'b',etc.i have searched around online a lot and have soaked up both data sheets of the Pic and Max chip so anything will be helpful.iam using a regular bread board.Any assistance is much appreciated.


The hardware schematics are (not surprisingly) on the Hardware page

Nigel's PIC Tutorial Hardware
I have a question about that same page, quote below:

This is the RS232 board, it uses a MAX232 5V to RS232 converter chip, this converts the 0-5V TTL levels at the PIC pins to the +12V/-12V levels used in RS232 links. As is common with these devices it inverts the data during the conversion, the PIC USART hardware is designed to take account of this - but for software serial communications you need to make sure that you invert both the incoming and outgoing data bits.

I am wondering about the inversion on the max232 and how it would effect the pic and computer, I do not see anything about this in the pic sheets. Even though it may work as good practice should an inverter be used?

Tnx, Mike.

Nigel Goodwin

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Most Helpful Member
Sry i must have missed that.and thanx 4 the very quick replies.Do the capacitor values vary from one pic to another?ive seen other schematics with different values.and can i use a serial to usb converter??
The capacitor values make little or no difference, they aren't in any way critical. Serial to USB should work fine, but bear in mind there's no handshaking, and serial/USB converters aren't generally very fast - but the 9600 baud in the tutorials should be fine


Serial to USB converters can be fast if you can stuff them with data fast enough, depends on the maker and how they implement it. If it does a single byte per transfer it's a waste of time, many have buffers and do bulk transfers if you can keep the buffers full, these can FAR surpass RS232 specs for baud rates.
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