Post by thread:RS232 COMM QUESTIONS

I WANT TO DO RS232 FROM MY COMPUTER TO A PIC16C65 OR 74. LOOKING AT THE MICROCHIP 94/95 CONTROL BOOK SECTION AN547 I WAS CONFUSED. I WANT TO BE ABLE TO SEND/RECIEVE DATA AT MY COMPUTER. I WAS PLANNING ON DOING ASYNCHRONOUS & USING A PARITY BIT. I WANT TO USE THE MAX-232 CHIP WHICH APPEARS TO ONLY HAVE TX & RX. SEEING THIS I ASSUME THAT I MUST USE THE SOFTWARE TX & RX POLLING EXAMPLES SHOWN IN THE BOOK. IN ORDER TO MAKE SURE THAT THE DATA IS GETTING RECIEVED AND TRANSMITTED CORRECTLY I ASSUME THAT I MUST DEVELOP SOME SORT OF HANDSHAKING LOGIC BETWEEN THE TWO. IF SOMEONE COULD CONFIRM MY ASSUMPTIONS PLEASE DO SO. I WAS THINKING ABOUT DOING CTS & RTS HANDSHAKING BUT WAS THINKING THIS WOULD MAKE MY LIFE MORE DIFFICULT. NOTE THAT SPEED IS NOT AN ISSUE. PLEASE COMMENT THANK YOU.

"Craig E. Gooder" <spam_OUTCraig.E.Gooder-2TakeThisOuTtc.umn.edu> wrote: > I WANT TO DO RS232 FROM MY COMPUTER TO A PIC16C65 OR 74. LOOKING AT THE Craig, firstly, please, pretty please, don't use all capital letters in your messages - it is *very* hard to read. And you want your messages to be read, not ignored. Using all caps is considered to be SHOUTING. Ok, enough of netiquette - as to your questions; it would be easier to give advice if you gave more info as to your actual application, but a few points; the MAX-232 (I prefer the pin-equivalent MAX-202 because it requires smaller (0.1uF) capacitors) has two transmit and two receive buffers. You can use them for any purpose you like. Obviously you will use one each for TX and RX data, so you have two left you can use for hardware handshaking if you like. Since the 16C74 has no dedicated serial handshake pins, you would just select two port pins to use for RTS/CTS handshaking if you go that way. But depending on what you are actually doing, it may not be necessary to use hardware handshaking. If for example you are sending data to the PIC and expecting some kind of response before you send the next block, that will be sufficient handshaking. As long as there is enough buffer space for the maximum size data block, you won't have a problem. Note that the PIC will have no trouble receiving the data at any reasonable rate (i.e. whatever the PC can send it at) as long as you are not doing any substantial processing of each data byte on the fly. A microcontroller like the PIC can easily produce or consume data at 115200 baud, in short bursts (because of limited RAM for buffering). That's about all that can be said without more detailed information. Clyde -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 .....clydeKILLspam@spam@hitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235 ---------------------------------------------------------------------------- For info on the World's best C cross compilers for embedded systems, point your WWW browser at http://www.hitech.com.au, or email infoKILLspamhitech.com.au

Craig, one more point; you say your concern is to ensure your data is received correctly; RTS/CTS handshaking will never guarantee that - at best it will prevent receiver overruns, but there are many other ways your data can be waylaid. You must implement some kind of error-checking and acknowledgement protocol between the two ends to ensure correct receipt of data. How complex this has to be depends on what you are doing. Clyde -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 .....clydeKILLspam.....hitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235 ---------------------------------------------------------------------------- For info on the World's best C cross compilers for embedded systems, point your WWW browser at http://www.hitech.com.au, or email EraseMEinfospam_OUTTakeThisOuThitech.com.au

Jim Main <jmainspam_OUTcqm.co.uk> wrote: > >a few points; the MAX-232 (I prefer the pin-equivalent MAX-202 because > >it requires smaller (0.1uF) capacitors) has two transmit and two > >receive buffers. > > If you spend a little more, you could use the MAX-233 which doesn't need any > external capacitors at all. A little more??? The pricing I have indicates that a MAX233 is about 2-3 times the price of a MAX202. That's an expensive way to buy capacitors! Clyde -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 @spam@clydeKILLspamhitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235 ---------------------------------------------------------------------------- For info on the World's best C cross compilers for embedded systems, point your WWW browser at http://www.hitech.com.au, or email KILLspaminfoKILLspamhitech.com.au

At 8:38 AM 5/25/96, Craig E. Gooder wrote: >I WANT TO DO RS232 FROM MY COMPUTER TO A PIC16C65 OR 74. LOOKING AT THE >MICROCHIP 94/95 CONTROL BOOK SECTION AN547 I WAS CONFUSED. I WANT TO BE >ABLE TO SEND/RECIEVE DATA AT MY COMPUTER. I WAS PLANNING ON DOING >ASYNCHRONOUS & USING A PARITY BIT. I WANT TO USE THE MAX-232 CHIP WHICH >APPEARS TO ONLY HAVE TX & RX. SEEING THIS I ASSUME THAT I MUST USE THE >SOFTWARE TX & RX POLLING EXAMPLES SHOWN IN THE BOOK. IN ORDER TO MAKE SURE >THAT THE DATA IS GETTING RECIEVED AND TRANSMITTED CORRECTLY I ASSUME THAT I >MUST DEVELOP SOME SORT OF HANDSHAKING LOGIC BETWEEN THE TWO. IF SOMEONE >COULD CONFIRM MY ASSUMPTIONS PLEASE DO SO. I WAS THINKING ABOUT DOING CTS >& RTS HANDSHAKING BUT WAS THINKING THIS WOULD MAKE MY LIFE MORE DIFFICULT. > NOTE THAT SPEED IS NOT AN ISSUE. PLEASE COMMENT THANK YOU. Maxim and other manufactures make 232 interface chips with more 232 lines. I'm using the 238 which has 4 in and 4 out.

Hi Clyde >> If you spend a little more, you could use the MAX-233 which doesn't need any >> external capacitors at all. > >A little more??? The pricing I have indicates that a MAX233 is about 2-3 times >the price of a MAX202. That's an expensive way to buy capacitors! If you take off the price of the capacitors, then it works out to about twice the price from my supplier - it's still an option if you want to save space or a bit of work in assembly though.. (also depends on who's paying for the project at the end of the day..ie, not me :-) Jim