RS-232 PIC16F1827

TCC · Joined: 10 Feb 2010 Posts: 9

Hi,

I have written a test program but I have problem trying to transmitting out correctly to my PC's COM port using rs-232.

The hyperterminal output shows

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Did you set Hyperterminal to 38400 baud ?

This is a new, enhanced 16F-series PIC. It's possible there are bugs
in the compiler. What's your compiler version ?

TCC · Joined: 10 Feb 2010 Posts: 9

Yes, my setting in HyperTerminal is correct.

I complied with MPLAB, PCM version 4.105

Ttelmah · Guest

The discrepancy, looks suspiciously like a factor of 8*.
Prove that your chip is running at 4MHz. Do the simple 'set a pin high', pause for half a second, set it low, pause again, repeat. Verify that you do see 1Hz. It is possible that the actual problem is the compiler setting up the oscillator wrong, and you are actually running at 500KHz.....
There is nothing in the UART section, that easily gives a factor of 8* error (the difference between the two prescalers is a factor of 4*), and the BRG calculation is the same as for most older chips. I'd be very suspicious that the oscillator may be the actual problem....
500KHz, is the _default_ setting of this chips oscillator. I suspect that the compiler is not changing the prescaler properly.
If it is running at 500K, you might try a separate 'setup_oscillator' line, or just set the prescaler yourself, while moaning at CCS....

Best Wishes

TCC · Joined: 10 Feb 2010 Posts: 9

Hi Ttelmah

Thanks for your suggestion, i have a line 'setup_oscillator(OSC_4MHZ)' and it work slightly better..but it still output garbage.

I measured the bit rate from the scope and found that low bit is 38.4KHz but high bit is 33.6KHz which does not tally with my baudrate.

Any further suggestion?

TCC · Joined: 10 Feb 2010 Posts: 9

Hi,

When running with external crystal (in HS mode), I found that the timing of this 1827 chip is always 4x faster of my settings.

For example, during delay_ms(500), i am getting 125ms instead of 500ms, my baud rate also 4x faster.

Please advice.

Ttelmah · Guest

Implies the PLL is getting turned on.....
Unfortunately, if this is turned 'on' in the fuses, it can't be turned off using the software enable/disable.
Does your programmer have the ability for you to look at/set the fuses from it's control window?. If so, sit down, and make a list of how the fuses should be set, qand manually change them here. If it then works, you know exactly what the problem is.....
It looks as if the fuse settings for this chip are completely screwed...

Best Wishes