Maxim Integrated MAXQ Family - Manual (Page 92)

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MAXQ Family User’s Guide
9.3.5 Overflow/Interrupt on Cumulative Time
To cause an overflow only when the T2P pin has been low for some cumulative duration, Timer 2 could be configured to the gated com-
pare mode of operation with an initial starting value appropriate for the cumulative duration to be detected.
; ------------------ Reset State: T2R = T2V = T2C = 0000h ------------------------
MOVE T2V, #1234h ; Overflow after T2P input low for (10000h-01234h) T2CLKs
MOVE T2CFG, #01110000b ; T2CI =0 (sysclk/N input)
; T2DIV[2:0] =111 (/128)
; T2MD =0 (16-bit)
; CCF[1:0] =00 (no edges)
; C/T2 =0 (timer/compare)
MOVE T2CNA, #10101001b ; ET2 =1 (enable Timer 2 ints)
; T2OE[0] =0 (input)
; T2POL[0] =1 (gating level = ‘1’)
; TR2L:TR2 =01 (start timer 2)
; CPRL2 =0 (no capture possible)
; SS2 =0 (not single-shot mode)
; G2EN =1 (gating enabled)
; ------------------ TF2 Interrupt : Cumulative low duration reached
T2P PIN
CODE EXECUTION:
POINT A
CODE EXECUTION:
POINT B
1A
1B
2A
2B
EVENTS:
1A: GATING CONDITION IS REMOVED; TIMER BEGINS TO RUN.
2A: TIMER 2 OVERFLOWS.
1B–2B: SAME SEQUENCE AS 1A–2A, EXCEPT THAT TIMER 2 STARTS RUNNING IMMEDIATELY SINCE IT IS NOT GATED.
Figure 9-8. Timer 2 Application Example—Overflow/Interrupt on Cumulative Time
Maxim Integrated