rs232 with hardware USART

[shadowlight69]

hi.
I just used the below code on a pic18f4550 with max232 chip, running a 20mhz crystal, and i am getting no communication at all in either direction

I have no clue what could be wrong. i tried anouther brand new ic, but to no avail.
I also read the pbp manual and couldn't find the answer there.
It would be very kewl to get this working.

Thanks.

Device = 18F4550
Xtal 20
DEFINE HSER_BAUD 9600
TRISB.6 = 0
TRISB.7 = 1
DEFINE HSER_ CLROERR 1
datain var Byte
main:
HSerIn [datain]
HSerOut [datain]
GoTo main
End

[DocDingwall]

Shadowlight69
I'm also facing the same issue (and have been stuck for weeks now). The main issue (so far as I can understand) is that the processor timing is more complicated with this family of chips. The processor in your case is probably not running at 20MHz. The way to tell is to set a loop to flash an LED with a longish pause between flashes (say "pause 5000" for instance) and see how long it actually takes to flash. If it is not 5 seconds then your processor is not running at 20 MHz. My problem is trying to figure out from the fuses what the processor IS running at.

Can I ask you to start this as a new thread? We'll get help quicker that way.

Thanks,
DD.

[Dave]

shadowlight69 , Is that the actual program you are trying to run? If so "Xtal 20" is not a command but, "DEFINE OSC 20" is.

Dave Purola,
N8NTA

[Archangel]

Just a reminder: Hardware serial port USART in PICs require a pull UP resistor to work as they send Data TRUE.

[Dave]

Joe S. , What? "Hardware serial port USART in PICs require a pull UP resistor to work " I have never heard of such a thing.. The USART port's on all of the MicroChip processors are capable of sinking as well as sourcing current... At least the last time I read them.... Better read your data sheet's Joe.

Dave Purola,
N8NTA

[Archangel]

Data TRUE idles high, Data inverted idles Low - Hserin receives data TRUE. Hardware usart receive is an input. It neither sources or sinks current, although there may be chips with internal pullups. I know the chips I have used will not receive without the pullup.

[Bruce]

If he has the PIC connected to a max232 hooked to a PC serial port the RX pin should already be held at logic 1 through the max232.

http://www.rentron.com/Files/bMAX232.gif

PIC to PIC using the hardware UART the tx pin on both will idle high so that works also without a pull-up. Even bit-banged serial should hold the tx pin at the idle logic state during idle periods.

But;
Device = 18F4550
Xtal 20

Indicates he's probably using the Proton compiler, so I would post the question there. It's most likely a configuration problem. Without config options in your code you're using whatever defaults they have in the include file, so it's probably not running at 20MHz.