Post by thread:Serial interface problem

I am puzzled why when I try to interface the transmit data line from an rs232 interface to a pic through a 10k resistor to RA1 why it ceases to operate. On a scope, the levels are a nice 5-0. Works fine with a max232. The only changes I've made are to replace the max232 chip with a 10k, and change my Rxdata define from RA1 to !RA1. I'm sure someone else has ran into this one. Craig

Craig Lee wrote: > > I am puzzled why when I try to interface the > transmit data line from an rs232 interface to > a pic through a 10k resistor to RA1 why it > ceases to operate. On a scope, the levels are > a nice 5-0. > > Works fine with a max232. The only changes > I've made are to replace the max232 chip > with a 10k, and change my Rxdata define from > RA1 to !RA1. if you now have [NOT] RA1 as above then the MAX232 should also NOT work ? are you programming in C ? else you will need to swap bcf and bsf instructions (and power on initialisation) to get equiv output states of max232. regards, Graham D. > > I'm sure someone else has ran into this one. > > Craig -- Steam engines may be out of fashion, but when you consider that an internal combustion engine would require recovery of waste heat by transfer just before top dead centre then fashion becomes rather redundant, USE STRATIFIED HEAT EXCHANGERS ! and external combustion. You heard it first from: Graham Daniel, managing director of Electronic Product Enhancements. Phone NZ 04 387 4347, Fax NZ 04 3874348, Cellular NZ 021 954 196.

It's not clear if you mean the PIC doesnt work, or if your code no longer does. Assuming the latter, I think you'll find that you need to invert your bits. i.e. the logic states are reversed without the max232. Paul At 06:02 PM 5/5/99 -0600, you wrote: {Quote hidden}>I am puzzled why when I try to interface the >transmit data line from an rs232 interface to >a pic through a 10k resistor to RA1 why it >ceases to operate. On a scope, the levels are >a nice 5-0. > >Works fine with a max232. The only changes >I've made are to replace the max232 chip >with a 10k, and change my Rxdata define from >RA1 to !RA1. > >I'm sure someone else has ran into this one. > >Craig Paul Davis Sr. Systems Engineer OEM, Carrier Sales, Healthcare spam_OUTpdavisTakeThisOuTnbase-xyplex.com http://www.nbase-xyplex.com 184 Shuman Blvd., Suite 200 Naperville, IL. 60563 Phone: 630-717-2960 x 3072 FAX: 630-357-4237

It works fine for the Hitech C compiler: main() { RA1 = !RA1; } compiles to: 19 ;c:\ht-pic\projects\misc\test.c: 5: RA1 = !RA1; 20 03FC 1283 bcf 3,5 21 03FD 3002 movlw 2 22 03FE 0685 xorwf 5 23 ;c:\ht-pic\projects\misc\test.c: 6: } Regards Mike Rigby-Jones {Quote hidden}> At 06:02 PM 5/5/99 -0600, you wrote: > >with a 10k, and change my Rxdata define from > >RA1 to !RA1. > > Sorry, ! will not work on a bit. You need at least a char. > > Cheers, > Bob > > http://www.bobblick.com/

HI, an idea: in this mode you should detecting a rising edge as a start bit instead of falling one. Did you? Imre On Wed, 5 May 1999, Craig Lee wrote: {Quote hidden}> I am puzzled why when I try to interface the > transmit data line from an rs232 interface to > a pic through a 10k resistor to RA1 why it > ceases to operate. On a scope, the levels are > a nice 5-0. > > Works fine with a max232. The only changes > I've made are to replace the max232 chip > with a 10k, and change my Rxdata define from > RA1 to !RA1. > > I'm sure someone else has ran into this one. > > Craig > >

For me 10k worked fine. Are you sure the problem is in the PC->PIC path? The edges of the signal could be a bit different now, so when your receive code was critical it could be just-off now. maybe have the PIC copy the in pin to the out pin in a loop and see whether you get an echo on the PC? Wouter. ---------- {Quote hidden}> From: Craig Lee <.....cleeKILLspam@spam@ATTCANADA.NET> > To: PICLISTKILLspamMITVMA.MIT.EDU > Subject: Serial interface problem > Date: Thursday, May 06, 1999 02:02 > > I am puzzled why when I try to interface the > transmit data line from an rs232 interface to > a pic through a 10k resistor to RA1 why it > ceases to operate. On a scope, the levels are > a nice 5-0. > > Works fine with a max232. The only changes > I've made are to replace the max232 chip > with a 10k, and change my Rxdata define from > RA1 to !RA1. > > I'm sure someone else has ran into this one. > > Craig

I think that the problem is in the code itself the function ! is a logical NOT and not bitwise. If you need to do bitwize then: - void main (void) void main (void) { unsigend char i; volatile unsigned char PORTVAL; i =~PORTVAL; //bits now inverted } Hope this helps, I am assuming that you're using C Dennis At 22:10 5/05/99 -0500, you wrote: >It's not clear if you mean the PIC doesnt work, or if your code no longer does. {Quote hidden}>Assuming the latter, I think you'll find that you need to invert your bits. >i.e. >the logic states are reversed without the max232. > >Paul > >At 06:02 PM 5/5/99 -0600, you wrote: >>I am puzzled why when I try to interface the >>transmit data line from an rs232 interface to >>a pic through a 10k resistor to RA1 why it >>ceases to operate. On a scope, the levels are >>a nice 5-0. >> >>Works fine with a max232. The only changes >>I've made are to replace the max232 chip >>with a 10k, and change my Rxdata define from >>RA1 to !RA1. >> >>I'm sure someone else has ran into this one. >> >>Craig > >Paul Davis >Sr. Systems Engineer >OEM, Carrier Sales, Healthcare >.....pdavisKILLspam.....nbase-xyplex.com >http://www.nbase-xyplex.com >184 Shuman Blvd., Suite 200 >Naperville, IL. 60563 >Phone: 630-717-2960 x 3072 >FAX: 630-357-4237 > >

I figure I should announce that I did fix the problem. The problem was that I was trying to just ! the bit and be happy. However, this doesn't seem to work bitwise or logically! So I did this (Reader's digest condensed version): #define RXNOTINV //rx bit is not inverted #ifdef RXNOTINV #ifdef RXNOTINV for(;;) { while(RXD == 0) continue; //delay 1/2 a bit if(RXD == 0) continue; //get a byte of data //delay to start of stopbit return ~c } #else for(;;) { while(RXD == 1) continue; //delay 1/2 a bit if(RXD == 1) continue; //get a byte of data //delay to start of stopbit return c } #endif Thanks, Craig > {Original Message removed}