Question on include files and problem with serial LCD/USB program

[Christopher4187]

Not sure if this means anything but if I don't define the oscillator "DEFINE OSC 20" and then I adjust the osc setting from HS to HSPLL the serout commands can stay in the program and the USB portion works. The only problem is now my LCD screen has garbage on it because the PIC isn't sending data at the right speed.

Correct me if I'm wrong but doesn't that mean that the PIC is working faster than it should because the OSC isn't defined. If so, is there a way to find the speed and adjust my LCD screen to match? Perhaps in the final design I should use a faster oscillator too.

[HenrikOlsson]

Hi,
Well, the manual says at least every 10ms... I wouldn't have expected 2ms either but if that what it takes then that is what it takes. I'm pretty sure THAT part has nothing to do with PBP really, it's just what's needed to have USB working.

As previosuly discussed the amount of time that your SEROUT2 statement takes at a certain baudrate depends on the amount of data. If RPM is 0-9 then you're sendning 3 bytes, if it's 10-99 you're sending 4 bytes, if it's 100-999 you're sedning 5 bytes and so on.

When you DEFINE OSC 20 (and asuming RPM needs 3 bytes) your SEROUT2 PORTD.3, $4054,[16,85,DEC RPM] statement will take 60/9600=6.25ms (+some for processing). If you RUN the PIC at 20MHz but doesn't tell the compiler that you are the compiler thinks it's running at 4MHz and calculates all the internal timing based on that. At 4MHz each cycles is 1us but at 20MHz each cycle is 200ns, the PIC is executing code 5 times faster then the compiler expected, your SEROUT2 statement is not sending at 9600baud, it's sending at 48000baud (or trying to, I don't think it'll actually work). So what previosuly took 6.25ms now only takes 1.25ms - which puts you inside the window for USBERVICE timeout.

Since you are running at 20MHz it's likely that SEROUT2 will work at 19200 or even 38400. At 38400 you're down to ~1.6ms for the above. You will need to check the documentation for your serial LCD if there's a way to change the buadrate. I'd expect some jumpers or dipswitches or perhaps it's software controlled. Do you have a link?

/Henrik.

[Christopher4187]

Since you are running at 20MHz it's likely that SEROUT2 will work at 19200 or even 38400. At 38400 you're down to ~1.6ms for the above. You will need to check the documentation for your serial LCD if there's a way to change the buadrate. I'd expect some jumpers or dipswitches or perhaps it's software controlled. Do you have a link?

/Henrik.

According to the datasheet, I can only use 9600 or 2400 baud. I bought a graphic LCD that will be here today but haven't looked at the documentation yet. The current screen I have is:

http://www.seetron.com/bpp420.html

The one I just bought is:

http://www.seetron.com/sgx120.html

Thanks again for the advice.

[HenrikOlsson]

Hi,
If you can't set the LCD to accept data at a faster rate then there's not much else to do than try to split the messages up. Perhaps you could do somethine like

Message VAR BYTE[20]
i VAR BYTE

ArrayWrite Message, [16, 85, DEC RPM, 0]
USBSERVICE
GOSUB SendIt

SendIt:
  i = 0
  While Message[i] <> 0
    USBSERVICE
    SEROUT2 Portd.3, $4054, Message[i]
    i = i + 1
  WEND
RETURN

That graphic LCD is also 9600baud max and my guess it needs even more data to be sent than the basic alphanumeric one so I wouldn't expect that to solve anything.

EDIT: Ooops, still 2.50...time for an upgrade perhaps? Since you learned to love using INLCUDE to structure your code you're going to like the conditional compilation features available in PBP3.