Post by thread:[PIC] Possible PLL problem with 18f452?

Hi guys! I've been monitoring the list every now and then (it is difficult to keep up) and I must say it's been the ultimate resource of ideas and debugging techniches for me. But this time I have a problem I can't figure out! I'm experiencing strange behaviour with the 452 and the PLL enabled: I have Timer0 creating a High Int every about 400us and in the ISR I load data to 4 HC373 latches (each one is selected by the output of a HC238 decoder), then point to 1 of 16 outputs via a HC154 and then exit the ISR (data latched is different each time). When I am using a 10MHz crystal with the PLL enabled (10Mhz clock) the code runs for about 2-3 seconds then hangs inside the ISR routine (I know it is in the ISR because I have a LED turned on when inside the ISR for debugging reasons). Even with a 4MHz crystal (4MHz clock) I get the same behaviour (without changing anything else the code). But, when I disable the PLL the code runs as expected without any lockup, even with a 20MHz crystal (that gives 5MHz clock, bigger than the 4MHz tested with the PLL). The date code of the chip is 0348 0J8, so it should be a C0 silicon revision, which is also what my programmer thinks because it reports rev 0x07. There is nothing in the errata for this (or previous) silicon revisions regarding the PLL. Am I doing something wrong? Thank you in advance for your answer and excuse my English! John Spiliotopoulos / Greece Below is the ISR code: ; LatchEn is PORTB, RC4 when high disables HC154 and enables HC238&HC373 ; DataPort is PORTD ; DecPort is PORTB and pins<3:0> connect to the inputs of HC154 and <1:0> to HC238 ; Also FSR0H is always set to 01 where a 4lines x 16rows data table exists HighInt: bsf LATA, RA0 ; Light up RA0 to indicate mode btfsc CurDisplayRow, 4 ; Check if CurDisplayRow overflowed to 17 clrf CurDisplayRow ; If yes, set it to 0 bsf LatchEn ; Set LatchEnable ; Routine to load buffers with data bcf DecPort, 0 ; Select buffer 00 bcf DecPort, 1 ; Select buffer 00 movff CurDisplayRow, FSR0L; Get current value of DisplayRow to FSR table movff INDF0, DataPort ; Send data to port bsf DecPort, 0 ; Select buffer 01 bsf FSR0L, 4 ; And also appropriate register movff INDF0, DataPort ; Send data to port bsf DecPort, 1 ; Select buffer 11 bsf FSR0L, 5 ; And also appropriate register movff INDF0, DataPort ; Send data to port bcf DecPort, 0 ; Select buffer 10 bcf FSR0L, 4 ; And also appropriate register movff INDF0, DataPort ; Send data to port ; This routine is needed to maintain the data on DecPort<7:4> bcf LatchEn ; Disable LatchEnable, displays Data movlw b'11100000' ; Value to mask andwf DecLatch, w ; AND it with current output xorwf CurDisplayRow, w ; XOR it with DisplayRow value movwf DecPort ; Get previous value of w to DecPort incf CurDisplayRow, f ; Increase CurDisplayRow to point to next Row bcf LATA, RA0 ; Exiting of DisplayUpdate mode, clear indicator bcf INTCON, TMR0IF ; Clear INT flag retfie FAST ; Return FAST -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>> I'm experiencing strange behaviour with the 452 and the PLL enabled: >You do know that the PLL on/off setting takes its (new) effect only after a power down - power up? Yes I do, I found out the hard way the first time I tried to use it :-) Each time I enable or disable the PLL I remove power and then reaply... Also I discovered another problem I can't figure out. The following code: movlw 'T' movwf TXREG a1: btfss PIR1, TXIF goto a1 movlw 'e' movwf TXREG b1: btfss PIR1, TXIF goto b1 movlw 's' movwf TXREG c1: btfss PIR1, TXIF goto c1 movlw 't' movwf TXREG d1: btfss PIR1, TXIF goto d1 movlw '-' movwf TXREG e1: btfss PIR1, TXIF goto e1 That should give "Test-" as a UART output gives only "Ts-"! Baud rate is 19.2Kbps. Even if I put it at a continous loop it keeps displaying "Ts-Ts-Ts-Ts-". The same code with a 877 in place of the 452 works fine. Could it be that my micro is damaged? How could that happen? John Spiliotopoulos/Greece -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Hey! I can finally contribute! From the datasheet (I am looking at the sheet for the 18f242 that I just finished the same type of project for): <quote> NOTE: TXIF is not cleared immediately upon loading data into the transmit buffer TXREG. The flag bit becomes valid in the second instruction cycle following the load instruction. </quote> therefore, your test at a1, which is the first instruction following the load, is testing TXIF before it gets updated from loading TXREG. Hope this helps! --Joe Jansen pic microcontroller discussion list <PICLISTKILLspamMITVMA.MIT.EDU> wrote on 03/05/2004 08:46:19 AM: > >> I'm experiencing strange behaviour with the 452 and the PLL enabled: > > >You do know that the PLL on/off setting takes its (new) effect only > after a power down - power up? > > Yes I do, I found out the hard way the first time I tried to use it :-) > > Each time I enable or disable the PLL I remove power and then reaply... > > Also I discovered another problem I can't figure out. The following code: {Quote hidden}> > movlw 'T' > movwf TXREG > a1: btfss PIR1, TXIF > goto a1 > movlw 'e' > movwf TXREG > b1: btfss PIR1, TXIF > goto b1 > movlw 's' > movwf TXREG > c1: btfss PIR1, TXIF > goto c1 > movlw 't' > movwf TXREG > d1: btfss PIR1, TXIF > goto d1 > movlw '-' > movwf TXREG > e1: btfss PIR1, TXIF > goto e1 > > That should give "Test-" as a UART output gives only "Ts-"! Baud > rate is 19.2Kbps. Even if I put it at a continous loop it keeps > displaying "Ts-Ts-Ts-Ts-". The same code with a 877 in place of the > 452 works fine. > > Could it be that my micro is damaged? How could that happen? > > John Spiliotopoulos/Greece > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

John wrote: > Hi guys! > > I've been monitoring the list every now and then (it is difficult > to keep up) and I must say it's been the ultimate resource of > ideas and debugging techniches for me. But this time I have a > problem I can't figure out! > > I'm experiencing strange behaviour with the 452 and the PLL enabled: > Are you using the regulatory 100nF caps close to the power pins? Are you using a small cap from the Mclr down to ground with a pullup on the pin? You might find it's noise on the supply / Mclr and the PLL draws that extra bit of current to tip it over the edge. Brian. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body