Timeline for Why am I getting the wrong timer frequency in PIC microcontroller application?
Current License: CC BY-SA 4.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 7, 2023 at 20:07 | answer | added | PStechPaul | timeline score: 1 | |
| Jun 7, 2023 at 14:47 | vote | accept | RickyBoy | ||
| Jun 7, 2023 at 10:09 | comment | added | RickyBoy | @PStechPaul: I would LOVE to be using a debugger. I tried to use the MPLAB debugger with my PICkit 3. But I had a horrible time. Some sort of error at every step. I went through all the steps in the Microchip docs, including their troubleshooters and got nowhere. On fora the best answer I could find was "your chip may not have debugging capabilities". At that point I went back to the sledgehammer approach and thought I would postpone using a debugger until I felt like learning more. Perhaps that will be my next cry for help in this forum!! | |
| Jun 7, 2023 at 0:00 | comment | added | PStechPaul | You might try using the software simulator to track the cause of the problem. The PICkit hardware debugger could be used as well. | |
| Jun 6, 2023 at 19:32 | answer | added | glen_geek | timeline score: 4 | |
| Jun 6, 2023 at 18:32 | comment | added | RickyBoy | Changed type long to unsigned short - results unchanged. YELLOW_LED still close to 1kHz, but RED_LED still @ 3.9kHz instead of 5kHz that I thought I would see. But nonetheless I'm grateful for the insight, thanks. I'm struggling to see why YELLOW behaves close to expected, but RED is far off. | |
| Jun 6, 2023 at 18:10 | comment | added | RickyBoy | OK, that's a very insightful comment... better, I infer, to use types int or smaller instead | |
| Jun 6, 2023 at 17:53 | comment | added | Jens | This is an 8 bit MCU and you use variables of type long, which need 4 memory read cycles to fetch the value. But the interrupt code may modify such a value in the middle of a read access of the main loop. Such variables must be declared as "volatile" and the access in the main thread must be surrounded by disable and enable interrupt calls. | |
| Jun 6, 2023 at 17:08 | comment | added | RickyBoy | Only remaining puzzle is why RED_LED blinks at 3.9kHz instead of 5kHz (conjecture in question was wrong)? | |
| Jun 6, 2023 at 16:50 | comment | added | RickyBoy | Correction: TIMER_RESET_VALUE = 158 | |
| Jun 6, 2023 at 16:40 | comment | added | RickyBoy | And disabling the prescaler and setting TIMER_RESET VALUE = 206 improves the frequency of YELLOW_LED to 975 Hz which is 2.5% off which should be fine. I can only increase the clock frequency on this chip externally. | |
| Jun 6, 2023 at 16:36 | comment | added | RickyBoy | @glen_geek. OK I found in datasheet that value of CMCON on POR/any reset is 0x00. Which by inference from your comment, is default active. Therefore, yes, setting CMCON = 0x07 has solved the problem. | |
| Jun 6, 2023 at 16:04 | comment | added | RickyBoy | @glen_geek, I was trying to figure something like that out from the datasheet but couldn't find it explicitly. Will try... | |
| Jun 6, 2023 at 16:03 | comment | added | RickyBoy | OK regarding (1)... in fact I believe there are two off-by-one problems... In the main while() loop I have been careless at when the YELLOW_LED is switched. I have forced it to switch when time_count == 4. This brings the frequeny of YELLOW_LED to 950 Hz (not sure if that's good enough but it's an explanation) Maybe there's some slippage in the instruction cycle as well? I will try disabling the prescaler. Regarding TMR0, it of course makes a small difference but I need to go back to the theory to know exactly what is the correct value. | |
| Jun 6, 2023 at 15:55 | comment | added | glen_geek | Is this a chip where the comparator is active by default? If you want RA1 to be a digital I/O, you might try disabling the comparator...CMCON=0x07. Haven't used this chip, so am unsure - this addresses the constantly-ON RED LED. | |
| Jun 6, 2023 at 15:37 | comment | added | Hearth | I'd write that as an answer, but I don't think I can help with 2), so it'd be an incomplete answer. | |
| Jun 6, 2023 at 15:29 | comment | added | RickyBoy | Ah! Could be! With prescaler at 1:2 you're right, I recall there should be an adjustment of 1. Let me try... | |
| Jun 6, 2023 at 15:21 | comment | added | Hearth | Could 1) be an off-by-one error? | |
| Jun 6, 2023 at 15:11 | history | asked | RickyBoy | CC BY-SA 4.0 |