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Hi,
I'm using a timer and external interrupt to detect the pulse, i can set the timer to run for 5 secs and loop back. But the program cannot vector to the external interrupt. This is my interrupt configurations and routine.
;******************************************** ;-----------INTERRUPTS CONFIGURATIONS-------- ;******************************************** MOV IE,#8CH MOV SWCINT,#000H MOV EIE1,#000H MOV EIE2,#000H MOV EIP1,#000H MOV EIP2,#000H MOV IP,#08H ;**************************** ;-Timer 1 Overflow Interrupt- ;**************************** T1_INT: CLR TF1 ; Clear overflow flag MOV TH1,#0D0H MOV TL1,#0A0H RETI ;********************** ;-External Interrupt 1- ;********************** EX_INT: INC 40H ; Increment 40H RETI
Does the input to the external interrupt need to be digital? Any advice would be nice... Thanks in advance.
Another thing. When measuring the pulse, you do not want to count # of heart beats in a fixed time interval. You want to measure the time between a fixed number of heart beats.
If you measure for 5 seconds, the start of the measurement period can start directly after a heart beat, but it can just as well start just before a heart beat.
In the same way, the 5 seconds can end just before or just after a heart beat.
This gives an error of +/- 1 heart beat during your 5 seconds, or a pulse error of +/- 12 bpm. Not too impressive, I would think.
This is the reason why a doctor who manually checks the pulse have to use a long time interval. You, on the other hand, have a high-quality clock available and can measure the exact number of milliseconds for a specific number of beat intervals.
But that requires you to start (or reset) the timer at a heart beat, and to stop (or read out) the timer after n more heart beats have been received.
I know what you are talking about. I can start the timer at the 1st peak, but i do not know how to stop the timer at the 2nd peak. Also the value in TH1 and TL1 are 8-bit each. How do i combine them together when the timer stops?
Let me think... hmm... Lets say i configured the timer in auto-reload mode and the external interrupt to detect falling edges already...
External_INT: SETB TR1
Like this i can only start the timer. I have no idea how to stop the timer. Any suggestions?