Triggering 5 TTL clocks simultaneously

[TurboLS]

OK, this code is written to wait for an interrupt, then clock out 784x512 bytes of data. The only chunk of the code shown is that which controls the clocking scheme. My question is if there is any way to execute time sensitive commands faster than the 1 usec instruction time. Thanks for all the help.

horizpulse var byte
vertpulse var byte

horizpulse = 1
vertpulse = 1
PORTB.0 = 0 ‘portb.0 is the Vphase1 clock
PORTB.1 = 0 ‘portb.1 is the Vphase2 clock
PORTB.2 = 1 ‘portb.2 is the Hphase1 clock
PORTB.3 = 0 ‘portb.3 is the Hphase2 clock
PORTB.4 = ‘portb.4 is the reset clock

buttonloop:
IF PushButtonOnPORTABIT2 = 1
THEN GOTO vertloop ‘waits for 5V that signals shutter is closed
ELSE GOTO buttonloop
vertloop:
horizpulse = 1
PORTB.0 = 1
PAUSEUS 139
PORTB.0 = 0
PORTB.1 = 1
PAUSEUS 139
PORTB.0 = 1
PORTB.1 = 0
PAUSEUS 139
PORTB.0 = 0
PAUSEUS 270
vertpulse = vertpulse + 1
IF vertpulse < 512
THEN GOTO horizloop
ELSE GOTO buttonloop
horizloop:
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
PORTB.3 = 0
PORTB.2 = 1
PAUSEUS 139
horizpulse = horizpulse + 1
IF horizpulse < 784
THEN GOTO horizloop
ELSE GOTO vertloop
END

[mister_e]

My question is if there is any way to execute time sensitive commands faster than the 1 usec instruction time

use a faster crystal.. depending of your PIC... some can run up to 40MHZ.

so in this case... 0.1 usec by SOME ASSEMBLER instruction

[TurboLS]

I was also toying with the idea of just setting the registers in one line, like

PORTA = %11001010

or something to that effect, but I have no idea how I would loop that.

[mister_e]

if you want to send 8 bits of data to PORTA in one shot... yes PORTA=MydataToSend will be what you need. Be sure that you have set the TRISA register before that
TRISA=255

[TurboLS]

Ok, here is my updated code, now I just have a few questions:

1.) Is there a way to split PORTA into analog and digital inputs?
2.) PORTB.4 is the reset clock and basically it has to be pulsing as soon as the microcontroller powers up. The problem is that once i start the other clocks, the time at which the reset goes high has to be in synch with H1 going low and H2 going high. In addition, it's high duration is 1/4 of the high time of the horizontal clocks. I will post up a timing diagram to explain what i mean later today. So basically I can't just put it in one of my loops, I have to start it pulsing at like a 25% duty cycle and when the other clocks are going, it has to be in synch with the horiztonals like i said earlier.

any help is appreciated.

' Connect analog input to (RA0)
' Connect clocks to PORTB
' PORTB.0 is the Vphase1 clock
' PORTB.1 is the Vphase2 clock
' PORTB.2 is the Hphase1 clock
' PORTB.3 is the Hphase2 clock
' PORTB.4 is the reset clock
' Connect pin 2 from the DB9 connector to PORTC.6
' Have a +5V source ready to touch PORTA.2 to trigger clocking process

include "modedefs.bas"

' Define ADCIN parameters
Define ADC_BITS 8 ' Set number of bits in result
DEFINE OSC 20 ' Sets clock speed to 20Mhz
Define ADC_CLOCK 4 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00000010 ' Set PORTA analog
TRISB = %00000000 ' Set PORTB to all output
Pause 500 ' Wait .5 second

Pause 500 ' Wait .5 second

horizpulse var byte
vertpulse var byte
adval var byte ' Create adval to store result

horizpulse = 1 ' Initialize counters, initial states
vertpulse = 1
PORTB.0 = 0
PORTB.1 = 0
PORTB.2 = 1
PORTB.3 = 0
PORTB.4 = 0

buttonloop:
IF PushButtonOnPORTABIT2 = 1
THEN GOTO vertloop ' Waits for 5V that signals shutter is closed
ELSE GOTO buttonloop
vertloop:
horizpulse = 1
PORTB.0 = 1
PAUSEUS 139
PORTB.0 = 0
PORTB.1 = 1
PAUSEUS 139
PORTB.0 = 1
PORTB.1 = 0
PAUSEUS 139
PORTB.0 = 0
PAUSEUS 270
vertpulse = vertpulse + 1
IF vertpulse < 512
THEN GOTO horizloop
ELSE GOTO buttonloop
horizloop:
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
PORTB.3 = 0
PORTB.2 = 1
PAUSEUS 50
ADCIN 0, adval ' A/D 8 bit value from PORTA.0 into adval
SEROUT2 PORTC.6,16416,[BIN8 adval,13,10] ' Output 8 bit word serially to PC from C.6
PAUSE 87
horizpulse = horizpulse + 1
IF horizpulse < 784
THEN GOTO horizloop
ELSE GOTO vertloop
END

[mister_e]

1.) Is there a way to split PORTA into analog and digital inputs?

for sure... see datasheet in the A/D section.. ADCON1 TABLE 19-2

will be interesting to have kind of flowchart and schematic for the other problems you have.

[Darrel Taylor]

TurboLS,

What version of PBP are you using? I've never seen this work in any versions I've had.

IF vertpulse < 512
THEN GOTO horizloop
ELSE GOTO buttonloop

I've wanted to use that type of syntax before, but I get nothing but errors. Did I miss an update or something. I have 2.45

Darrel

[TurboLS]

I am using 2.46 and I will have a pic up soon that has the timing scheme. thanks for the replies.

[TurboLS]

here is the timing diagram. notice how the reset, H1, and H2 are in synch at the lower right. Also notice that the reset is going all the time, even when the other 4 clocks are not.

please click the link and scroll to page 13

http://www.kodak.com/global/plugins/...2ELongSpec.pdf

thanks.

[TurboLS]

Oh yeah, i am gettin some errors from that if else stuff too.... gonna have to find a way around that arghhhh!

scratch that, you just have to put all the commands on the same line, like so:

IF vertpulse < 512 THEN GOTO horizloop ELSE GOTO buttonloop

however, i still have 9 errors to fix before mine compiles properly.

[TurboLS]

Also, I tried looking at the ADCON1 register, and i guess if I am reading from the table properly... to set PORTA.2 to digital in, I should say ADCON1 = %00001101 cuz that's where the D and the AN2 meet.

I am still having a problem with the OnPushButton command and apparently I have to use END IF commands, which I am not sure how I will implement just yet.

[TurboLS]

I got it down to 6 errors, all with my IF statements. Here is what I have for a generic IF line:

IF PushButtonOnPORTABIT2 = 1 THEN GOTO vertloop ELSE GOTO buttonloop

on the following line i have

ENDIF

and doing that got rid of 3 of the errors, but now I need to figure out why it doesn't like my then goto / else goto commands.

For each of my 3 if statements, I get

bad expression
bad expression or missing then

[TurboLS]

OK, i know i have been posting a lot lately, but now i am down to 2 errors, both associated with

IF PushButtonOnPORTABIT2 = 1 then

I think it has something to do with me setting the ADCON1 register incorrectly.

[TurboLS]

OK, I fixed it (I think) to where I have no compiler errors.

basically I had to change the above line to

IF PORTA.2 = 1 then

[mister_e]

IF vertpulse < 512 THEN GOTO horizloop ELSE GOTO buttonloop

I prefer like this

IF vertpulse < 512 THEN 
    GOTO horizloop 
ELSE 
    GOTO buttonloop
ENDIF

Using Alias to i/o

TRISA = 255 ' Set PORTA as input

PushButton1 var PORTA.0
PushButton2 var PORTA.1
PushButton3 var PORTA.2

IF PushButton1 then ' Same as PushButton=1
   ' do your stuff here
ENDIF

[TurboLS]

So yeah I am still stuck with the whole reset clock thing. Is there a way I can generate a clock in hardware that is not a 50% duty cycle? By using one of the timer functions perhaps?

I was also wondering approximately how fast each of the commands in my program would take to process. Knowing that, I would be able to generate the reset clock by estimating the time in usecs.

thanks again for all the input.

[mister_e]

One thing i figure is to use the OSCLKO pin and connect to RB0 or else interrupt source. Once you'll be the in the interrupt routine, you'll be able to do everything. Generate all your delay and pin level. Will be a bit tricky to get the perfect timing but not impossible.

If you want to generate a 4MHZ clock, you'll need a 8MHZ crystal. Interrupt on rising or falling edge. Interrupt routine will generate your R, H1 and H2 frequency in one shot.

Depending your crystal speed, your instruction will be executed in few msec or less.

BUT for that kind of stuff where accuracy and precision is important, you'll probably need to do your delay and some test in assembler. Assembler instruction can be executed in 1 or 2 frequency cyle. Let's say at 8MHZ, 1 intruction every (1/(8Mhz/4)) = 0.5 uSec. Can be usefull to have a PIC who have an internal PLL to multiply your cystal speed.

If you have a 8MHZ crystal, execution time will be 4 times faster so from 0.5uSec to 0.125 uSec.

[TurboLS]

The reset, H2, and H1 will be about 3.6kHz. I don't know if there is a way I can get that with the multipliers.

Is there like a table where I can calculate the execution times? I know that "time-sensitive" commands take 1 usec with a 20Mhz clock (which is what I am using).

How long do if statements and such take, jumps to different parts of the program (like when I use the GOTO commands)?

[mister_e]

if they are constant... you can use HPWM on 2 channel... 2 different duty but the same frequency. They will run in background and they will not be interfered by anything else.

OR you can use the internal TIMER1 16bit and do you delay stuff when you get TIMER1 overflow interrupt.

at 3.6 KHZ period = 277.777 uSec

let's say you'll use a 20Mhz crystal... internal frequency 5MHZ period = 0.2 uSec = 1388.888 internal clock count. We want to change state every 1/2 period. 1388.888 uSec / 2 = 694.4444 uSec. So you'll have to preload Timer1 to 65535-694 = 64841 or $FD49.

here's a snippet to produce 3 different duty cycle with TIMER1

' program to generate Multiple duty cycle @ 5 mhz on PORTC
' Use of PIC18F2220
'
@ __CONFIG _CONFIG1H, _HS_OSC_1H 
    '  HS 

@ __CONFIG _CONFIG2L, _BORV_20_2L & _BOR_ON_2L & _PWRT_ON_2L
    '  BOR Voltage - 2.0v
    '  Brown-Out Reset enabled
    '  Power-Up Timer enabled
    
@ __CONFIG _CONFIG2H, _WDT_ON_2H
    '  Watch Dog Timer enabled

@ __CONFIG _CONFIG3H, _MCLRE_ON_3H & _PBAD_DIG_3H & _CCP2MX_ON_3H & _CCP2MX_B3_3H
    '  MCLR enabled
    '  PORTB<4:0> pins reset as digital pins
    '  CCP2 pin function on RC1
    '  CCP2 pin function on RB3 (alt defn)

@ __CONFIG _CONFIG4L, _DEBUG_OFF_4L & _LVP_OFF_4L & _STVR_ON_4L
    '  DEBUGger disabled
    '  Low Voltage Prgramming disabled
    '  Stack over/underflow Reset enabled

@ __CONFIG _CONFIG5L, _CP0_OFF_5L & _CP1_OFF_5L
    '  Block 0 readable/ may be writable 
    '  Block 1 readable/ may be writable

@ __CONFIG _CONFIG5H, _CPB_OFF_5H & _CPD_OFF_5H
    '  Boot Block readable / may be writable 
    '  Data EE memory readable / may be writable

@ __CONFIG _CONFIG6L, _WRT0_OFF_6L  & _WRT1_OFF_6L
    '  Block 0 writable
    '  Block 1 writable

@ __CONFIG _CONFIG6H, _WRTC_OFF_6H & _WRTB_OFF_6H & _WRTD_OFF_6H
    '  Config registers writable
    '  Boot block writable
    '  Data EE writable 

@ __CONFIG _CONFIG7L, _EBTR0_OFF_7L & _EBTR1_OFF_7L
    '  Block 0 readable
    '  Block 1 readable

@ __CONFIG _CONFIG7H, _EBTRB_OFF_7H
    '  Boot block readable
    
    DEFINE OSC 20 
    TRISC=0
    INTCON = %01000000 ' enable peripheral interrupt
    PIE1 = %00000001   ' enable TIMER1 overflow interrupt
	TMR1L=$49
	TMR1H=$FD
    T1CON = %00000101 ' prescaler 1:1
    				  ' Clock source = Fosc/4
    				  ' start the timer1
    on interrupt goto TMR1_Overflow
    Passes	var	bit
    clear
START: 
    goto start
    
disable
TMR1_Overflow:
    T1CON.0=0 'stop timer
    PIR1.0=0 ' reset interrupt flag
    TMR1l=$49
	TMR1H=$FD
    T1CON.0=1 'start timer
	if Passes then
    	PORTC = 6
    	pauseus 69
    	PORTC = 4
    	passes= 0
	else
       	PORTC = 1
    	passes= 1
    endif
    resume
enable

you may need to adjust the value of the TIMR1L to fine tune your frequency.

To calculate or to know the time an instruction take, you can use MPLAB's stopwatch... give a great aprox of the time.

[TurboLS]

I was thinking of doing the reset on one of those HWPM things because the reset is the only constant clock. Then I could just do a conditional statement to make sure that the reset and the horizontal clocks are in synch. The good thing about that, like you said, it would run in the background and so I could run all the other clocks just as I had them. What do you think??

[mister_e]

Then I could just do a conditional statement to make sure that the reset and the horizontal clocks are in synch

mmm, IMO you can't check with internal to synchronize them. I figure you'll have to use an extra i/o to read from the PWM output. Once you get the highlevel or interrupt, you do your Horizontal stuff. A microsecond or less of
delay between to rising edge of Reset and your Horizontal... but at 3.6KHZ i can't figure it will be a big problem.

[TurboLS]

So you're saying something like:

IF PWM output is high, start the horizontal clocks

Yeah, using another I/O pin is not a problem, cuz at this point i think i am using 2 pins of portA

How would I go about getting the HPWM to oscillate at 3.6kHz with a 25% duty cycle? I will look at the manual again later today or tomorrow probably and see if i can figure it out.

thanks again, you are a huge help.

[mister_e]

it's a bit more than if pin is high... IF the according pin is at the rising edge of the signal... this ensure the right timing. Use interrupt source INT0, INT1 or else you can have on the rising edge... will be really easy now. The only thing you have to care about is the timing and latency in the other routines to get interrupt as quick as possible.

For the HPWM frequency and duty cycle, try

HPWM 1,64,3600 ' supposed to send HPWM 3.6KHZ at 25% duty

i don't know how accurate it will be. In my purpose i always set all the register myself. In your datasheet they tell you how to calculate everything.

[TurboLS]

What pin would that HPWM be coming off of??

[mister_e]

HPWM channel = CCP1 of your 18F4520 = PIN RC2 PIN 17

[TurboLS]

So I guess I could have it running in the background, then when I want to start the horizontal clocks, I could do an ON INTERRUPT command to make sure it is on the rising edge of the Reset HWPM clock.

[mister_e]

you don't have to make sure it's on the rising edge. Interrupt will do it for you. When you set your interrupt you can select rising or falling edge.

[TurboLS]

And I set that in the registers, right? And then I can run a wire from PIN 17 to an interrupt pin and do an ON INTERRUPT command? Would it look something like this or totally different? I am going to try and find some examples.

horizloop:
ON INTERRUPT
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
PORTB.3 = 0
PORTB.2 = 1
PAUSEUS 50
ADCIN 0, adval ' A/D 8 bit value from PORTA.0 into adval
SEROUT2 PORTC.6,16416,[BIN8 adval,13,10] ' Output 8 bit word serially to PC from C.6
PAUSE 87
horizpulse = horizpulse + 1
IF horizpulse < 784

[mister_e]

NOP...

i'll have more spare time tomorrow for that... BUT have a look on this thread download the code i did. It use the interrupt on an pin to do specific task. Can be handy to start. Code is well documented.

ON INTERRUPT GOTO define the place to go when an intterupt happen. See PBP manual on that statement. care will have to be made in the interrupt routine too. sould not be too loang... at minimum less than the time between each interrupts.

[TurboLS]

Well I would think I would only need one in the loop, just to make sure the Reset(HWPM) and Horizontal 2 are on their rising edge as in synch as possible.

[TurboLS]

What if I did something like this??

horizloop:
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
ENABLE
ON INTERRUPT GOTO H2lock
DISABLE
PAUSEUS 15
ADCIN 0, adval ' A/D 8 bit value from PORTA.0 into adval
SEROUT2 PORTC.6,16416,[BIN8 adval,13,10] ' Output 8 bit word serially to PC from C.6
PAUSEUS 87
horizpulse = horizpulse + 1
IF horizpulse < 784 THEN
GOTO horizloop
ELSE
PAUSEUS 270
GOTO vertloop
ENDIF

H2lock:
PORTB.3 = 0
PORTB.2 = 1
RESUME

[mister_e]

NOP, On Interruot goto is placed at the header of your code before your main loop. Since it's working in background, it will jump by himself to the interrupt routine. did you look at my previous link?

INTCON and probably others have to be set for interrupt type/source.

i'll make something like this later today.

[TurboLS]

What do you think of something like this>?

' Connect analog input to (RA0)
' Connect clocks to PORTB
' PORTB.0 is the Vphase1 clock
' PORTB.1 is the Vphase2 clock
' PORTB.2 is the Hphase1 clock
' PORTB.3 is the Hphase2 clock
' PORTB.4 is the reset clock
' Connect pin 2 from the DB9 connector to PORTC.6
' Have a +5V source ready to touch PORTA.2 to trigger clocking process

include "modedefs.bas"

' Define ADCIN parameters
Define ADC_BITS 8 ' Set number of bits in result
DEFINE OSC 20 ' Sets clock speed to 20Mhz
Define ADC_CLOCK 4 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

ON INTERRUPT GOTO H2lock ' When Reset clock is high
INTCON1 = %1001000 ' Enable RB0 Interrupt
INTCON = $80 ' Disables Interrupts
TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00001101 ' Set PORTA analog, except for pin 2
TRISB = %00000000 ' Set PORTB to all output
Pause 500 ' Wait .5 second
Pause 500 ' Wait .5 second

horizpulse var byte
vertpulse var byte
adval var byte ' Create adval to store result

horizpulse = 1 ' Initialize counters, initial states
vertpulse = 1
PORTB.0 = 0
PORTB.1 = 0
PORTB.2 = 1
PORTB.3 = 0
PORTB.4 = 0

buttonloop:
IF PORTA.2 = 1 then
GOTO vertloop
else
GOTO buttonloop ' Waits for 5V that signals shutter is closed
ENDIF
vertloop:
horizpulse = 1
PORTB.0 = 1
PAUSEUS 139
PORTB.0 = 0
PORTB.1 = 1
PAUSEUS 139
PORTB.0 = 1
PORTB.1 = 0
PAUSEUS 139
PORTB.0 = 0
PAUSEUS 270
vertpulse = vertpulse + 1
IF vertpulse < 512 THEN
GOTO horizloop
ELSE
GOTO buttonloop
ENDIF
horizloop:
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
INTCON = $80 ' Re-enables interrupts
PAUSEUS 15
ADCIN 0, adval ' A/D 8 bit value from PORTA.0 into adval
SEROUT2 PORTC.6,16416,[BIN8 adval,13,10] ' Output 8 bit word serially to PC from C.6
PAUSEUS 87
horizpulse = horizpulse + 1
IF horizpulse < 784 THEN
GOTO horizloop
ELSE
PAUSEUS 270
GOTO vertloop
ENDIF

DISABLE
H2lock:
PORTB.3 = 0
PORTB.2 = 1
RESUME
ENABLE
END

[TurboLS]

Also, I saw a blurb in the PBP manual about the fact that I can check the interrupt flag without actually enabling interrupts. If I did it that way, then I could merely do a check condition statement, similar to this, right?:

IF PORTB.2 = 1 AND INTERRUPTFLAG = 1 ' When horizontal 1 is high and reset is high

' Do the H1 > low, H2 > high, ADC conversion and the SEROUT2

[TurboLS]

OK, I checked the datasheet and the interrupt flag bit is bit 1 of the INTCON register. It also says that I have to reset it in software once an interrupt has occurred. So I was thinking if I just set the INTCON.1 = 0 right before the condition statement, then I could just wait until the INTCON.1 = 1 before clocking the horizontals. What do you think?

[Bruce]

Yep. I do this all the time.

Disable global interrupts (INTCON.7 = 0), and just monitor & reset interrupt flags as needed. Very handy.

[TurboLS]

Should I still enable the INTCON1 register? I have it set to %1001000 to use the RB0 interrupt. I have the HWPM (which is to be the interrupt source) set as follows:

HPWM 1,64,3600 ' Supposed to send HPWM 3.6KHZ at 25% duty

[TurboLS]

I tried compiling that and I get

Symbol not previously defined (INTCON1)

The updated code is as follows:

' Connect analog input to (RA0)
' Connect clocks to PORTB
' PORTB.0 is the Vphase1 clock
' PORTB.1 is the Vphase2 clock
' PORTB.2 is the Hphase1 clock
' PORTB.3 is the Hphase2 clock
' The reset will be connected to a HWPM clock pin #17
' Connect pin 2 from the DB9 connector to PORTC.6
' Have a +5V source ready to touch PORTA.2 to trigger clocking process

include "modedefs.bas"

' Define ADCIN parameters
Define ADC_BITS 8 ' Set number of bits in result
DEFINE OSC 20 ' Sets clock speed to 20Mhz
Define ADC_CLOCK 4 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

HPWM 1,64,3600 ' Supposed to send HPWM 3.6KHZ at 25% duty

INTCON1 = %1001000 ' Enable RB0 Interrupt
INTCON.7 = 0 ' Disables global interrupts
TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00001101 ' Set PORTA analog, except for pin 2
TRISB = %00000000 ' Set PORTB to all output
Pause 500 ' Wait .5 second
Pause 500 ' Wait .5 second

horizpulse var byte
vertpulse var byte
adval var byte ' Create adval to store result

horizpulse = 1 ' Initialize counters, initial states
vertpulse = 1
PORTB.0 = 0
PORTB.1 = 0
PORTB.2 = 1
PORTB.3 = 0

buttonloop:
IF PORTA.2 = 1 then
GOTO vertloop
else
GOTO buttonloop ' Waits for 5V that signals shutter is closed
ENDIF
vertloop:
horizpulse = 1
PORTB.0 = 1
PAUSEUS 139
PORTB.0 = 0
PORTB.1 = 1
PAUSEUS 139
PORTB.0 = 1
PORTB.1 = 0
PAUSEUS 139
PORTB.0 = 0
PAUSEUS 270
vertpulse = vertpulse + 1
IF vertpulse < 512 THEN
GOTO horizloop
ELSE
GOTO buttonloop
ENDIF
horizloop:
INTCON.1 = 0 ' Resets interrupt flag to 0
Resetcheck: ' Loops back to make sure
PAUSEUS 2 ' the PORTB.2 goes low and
IF INTCON.1 = 0 THEN ' PORTB.3 goes high as close
GOTO Resetcheck ' to the external trigger's
ELSE ' rising edge as possible
ENDIF
PORTB.2 = 0
PORTB.3 = 1
PAUSEUS 139
PORTB.3 = 0
PORTB.2 = 1
PAUSEUS 15
ADCIN 0, adval ' A/D 8 bit value from PORTA.0 into adval
SEROUT2 PORTC.6,16416,[BIN8 adval,13,10] ' Output 8 bit word serially to PC from C.6
PAUSEUS 87
horizpulse = horizpulse + 1
IF horizpulse < 784 THEN
GOTO horizloop
ELSE
PAUSEUS 270
GOTO vertloop
ENDIF
END

[Bruce]

There is no INTCON1 register. That would be why you get the error. Look at your datasheet.

To monitor interrupt "flag bits" you do not need to enable any interrupt enable bits or global interrupts.

Any event or condition that will trigger the interrupt, will set the interrupts flag bit. This happens regardless of whether you have "any" interrupt enabled or disabled.

A "Flag bit" indicates that an interrupt event occurred.

The interrupt "Enable bit" allows program execution to branch to the interrupt vector address (if global interrupts are enabled) when the flag bit is set by the event that caused the interrupt.

You can setup the RB0/INT0 on the 18F4520 to set the interrupt flag bit on a low-to-high or high-to-low transition on RB0/INT0. See the datasheet under INTCON2.

Then all you need to do is monitor INTCON.1 (this means INTCON register bit #1 NOT INTCON1) which is the "flag bit" inidicating the transition (event) on RB0/INT0 has occured.

After reading this bit, then reset it (clear it to 0) so you can check it again later to see if the event has happend again.

[TurboLS]

OK, I checked the manual and bit 6 controls the external 0 flag. I set it to '1' for the rising edge.

INTCON2 = %0100000 ' External Interrupt Flag on Rising Edge

Do I have to set the PORTB pull up enable bit?

Also, RB0 will be read as an input (wired from the HWPM pin 17), so I will have to reconfigure my TRISB register to accept an input on PORTB, right?

thanks again for the help.