Blinky on Lab-X1 twice as fast on 16F877 as on a 18F4550

Code on 16F877:

Code:

---

#CONFIG
    __config _HS_OSC & _WDT_OFF & _WRT_OFF & _BOREN_ON & _LVP_OFF  & _CPD_OFF & _PWRTE_ON & _DEBUG_OFF
#ENDCONFIG

DEFINE  OSC 20

INCLUDE "ALLDIGITAL.pbp"        ; Set all pins as digital

TRISD = %00000000
PORTD = %00000000

PAUSE  1000     

START:  PORTD = %10101010
        PAUSE  1000     
        PORTD = %01010101
        PAUSE  1000     

        GOTO    START
Finish: end

---

Code on 18F4550:

Code:

---

#CONFIG
    CONFIG    PLLDIV=5, CPUDIV=OSC1_PLL2, USBDIV=2, FOSC=HSPLL_HS
    CONFIG    PWRT=ON, BOR=ON, BORV=1, VREGEN=ON, WDT=OFF
    CONFIG    CCP2MX=ON, PBADEN=OFF, LPT1OSC=OFF, MCLRE=ON
    CONFIG    STVREN=ON, LVP=OFF, ICPRT=OFF, XINST=OFF
#ENDCONFIG

DEFINE OSC 48

INCLUDE "ALLDIGITAL.pbp"        ; Set all pins as digital

TRISD = %00000000
PORTD = %00000000

PAUSE  1000     

START:  PORTD = %10101010
        PAUSE  1000     
        PORTD = %01010101
        PAUSE  1000     

        GOTO    START
Finish: end

---

Close-up of jumpers on Lab-X1:

Attachment 9381


Lab-X1 oscillator jumpers:

Attachment 9382


The only difference between the 2 MCUs are the CONFIG and DEFINE OSC statements.


I'm at a loss to explain what I'm doing wrong here. Whatever I'm doing wrong, I've been doing it for a very long time.

Robert
I can't see the forest with all those trees standing in the way.

Test 1, slow 16F877 to 4 MHz:

Code:

---

#CONFIG
    __config _XT_OSC & _WDT_OFF & _WRT_OFF & _BOREN_ON & _LVP_OFF  & _CPD_OFF & _PWRTE_ON & _DEBUG_OFF
#ENDCONFIG

DEFINE  OSC 4

---

Lab-X1 jumper A=23

Nothing...


Go back to HS @ 20MHz with jumper A=12:

Back to twice as fast as it should...

Really puzzled, I expected it to run perfectly at 4 MHz.

Report here of some old PICs having been issued with 4 MHz max rating here:

https://www.embeddedrelated.com/show...ist/2282-1.php


I checked, mine are all ...-20.

Test 2, set all ports on 16F877 as output:

Code:

---

TRISA = %00000000
TRISB = %00000000
TRISC = %00000000
TRISD = %00000000
TRISE = %00000000

PORTA = %00000000
PORTB = %00000000
PORTC = %00000000
PORTD = %00000000
PORTE = %00000000

---

No difference, still blinking at twice the expected rate...


Robert

Do you have any means to check the real frequency oscillator output that is going to the PIC?

Also, JP3 does no look that is is correctly connected. PIC should be on the midle pin and the jumper select either 4MHz or the CLK output of the chip U2.

If Y1A out pin is the PIC clock input, then this pin will always get 4MHz as the diagram shows no matter what the other jumpers are at.

Correct me if I am wrong, but on that diagram seems to me that way.

Ioannis

Quote:

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Originally Posted by Ioannis

... Also, JP3 does no look that is is correctly connected. PIC should be on the midle pin and the jumper select either 4MHz or the CLK output of the chip U2.

If Y1A out pin is the PIC clock input, then this pin will always get 4MHz as the diagram shows no matter what the other jumpers are at.

Correct me if I am wrong, but on that diagram seems to me that way.

Ioannis

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Y1A is not populated on the Lab-X1. You can add an IC if you wish to replace the default setup. Taken fron LABX1.TXT:

Quote:

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... To select a 20MHz clock, jumpers A and B should be on pins 1 and 2 and jumper C should be on pins 2 and 3.

Jumper JP3 (not populated) allows a crystal or TTL or CMOS oscillator to be used directly without the ISC502M clock generator. A TTL or CMOS oscillator, Y1A, may be used in place of crystal Y1 and the 2 capacitors, C5 and C6.

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Having the jumper on the top 2 pins completes the circuit from ICS502M towards OSC1 (referred to as O1).

Robert

Quote:

---

Originally Posted by Demon

Test 2, set all ports on 16F877 as output:

Code:

---

TRISA = 000000
TRISB = 000000
TRISC = 000000
TRISD = 000000
TRISE = 000000

PORTA = 000000
PORTB = 000000
PORTC = 000000
PORTD = 000000
PORTE = 000000

---

No difference, still blinking at twice the expected rate...


Robert

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Don't you have to make one of the External Oscillator pins an Input in the TRISx Register? I'm on the road and can't look at the Data Sheet.

On those old chips like the 16F877, OSC1 and OSC2 aren't part of PORTA.

Quote:

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Originally Posted by mpgmike

Don't you have to make one of the External Oscillator pins an Input in the TRISx Register? I'm on the road and can't look at the Data Sheet.

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Pretty sure I saw that on USART pins.

Robert