In SX Microcontrollers, SX/B Compiler and SX-Key Tool, jdemeyer wrote:

I experimented with this idea.

I set Timer 1 up in Capture/Compare mode.  The Compare register is set to $ffff.  When Timer 1 reaches $ffff, it toggles RB.6 (i.e., low-high-low).  This pulse should happen approximately every 1.3 ms (20nS/pulse * 65536 pulses = 1.3 ms).
I set Timer 2 up in External Event Mode.  In this mode, Timer 2 counts pulses on RC.3.  I physically connect RB.6 (from Timer 1) to RC.3 (the external input for Timer 2) and Timer 2 counts the number of times Timer 1 reaches $ffff.  I set Timer 2's Compare register to $0bf0 (2288 decimal) and set up for an interrupt when the Compare register and Timer 2 match.  The interrupt should occur approximately every three seconds (2288 * 1.3 ms=2.99 s).
After the SX48 is programmed, there is a two minute time period in which nothing happens.  I set a break point as indicated in the code and there is no interrupt.  After two minutes, the interrupt begins to occur regularly but not at the designed time of three seconds.  It happens about every six seconds.

1.  Why might there be a two minute delay before the code begins to operate as expected?
2.  Why does the interrupt occur every six seconds rather than every three seconds?

Thanks,

Joe

[code]
DEVICE	SX48,OSCHS1
FREQ	50000000

INTERRUPT
	GOSUB DoSomething
T2R1CMH=$08
T2R1CML=$f0
T1R1CMH=$ff
T1R1CML=$ff

RETURNINT

AFlag VAR Byte

PROGRAM Start
DoSomething:
	IF AFlag=1 THEN	'break point set here
		AFlag=0
	ELSE
		AFlag=1
	ENDIF

RETURN

WATCH AFlag,8,UDEC

Start:
LVL_B=%00000000
LVL_C=%00000000
PLP_B=%01000000
PLP_C=%00000111
TRIS_B=%10111111	'RB.6 is an output
TRIS_C=%11111000	

RC=%00000000

AFlag=1

T2CNTA=%00000100	'interrupt on compare
T2CNTB=%00100011	'timer unrelated,edge detection,divide by one,external clock
T2R1CMH=$08
T2R1CML=$f0
'$08,$F0  This is every three seconds

T1CNTA=%00000000	'disable interrupts on timer 1
T1CNTB=%00000010	'timer unrelated,edge detection,divide by one,capture/compare
T1R1CMH=$ff
T1R1CML=$ff
'RB.6 toggles

Main:
	GOTO Main

END
[/code]

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