Using Timers in the MAXQ Famil

文章摘要：Output enables should be turned on before or at the same time as the run enable. Setting the run enable before the output enable can cause the output to be inverted since it is possible for interrupts to cause the code to be suspended (while the interrupt is serviced) in between the time the timer i

Using Timers in the MAXQ Famil,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com
Output enables should be turned on before or at the same time as the run enable. Setting the run enable before the output enable can cause the output to be inverted since it is possible for interrupts to cause the code to be suspended (while the interrupt is serviced) in between the time the timer is set to run and when the output enable is asserted. This can cause a compare or overflow event to happen before the output is enabled, which causes the output to be of the opposite polarity. This usually happens with the B or secondary output since the output enable (T2OE1) is in the T2CNB register while the run bit (TR2) and low run bit (TR2L) are in the T2CNA register. In this case the T2CNB register should be set up first or the T2CNA register should be set up with the run bits set to zero and then set the run bits after all registers have been configured.

Appendix: Table of bit settings for various modes

MODE	T2MD	C/T2	CCF[1:0]	T2OE[0]	T2OE[1]	T2POL[0]	T2POL[1]	G2EN	SS2	CPRL2
16 bit compare with optional gating	0	0	00	0 = primary output not enabled	0 = secondary output not enabled 1 = secondary output enabled	Defines gating level 0 = low 1 = high	Defines initial polarity of secondary output 0 = low 1 = high	0 = no gating 1 = gating enabled on primary pin	1 = Single shot 0 = use TR2 for run	0 Not used
16 bit compare with primary output enabled (no gating available)	0	0	00	1 = primary output enabled	0 = secondary output not enabled 1 = secondary output enabled	Defines initial polarity of primary output 0 = low 1 = high	Defines initial polarity of secondary output 0 = low 1 = high	0 Not usable with primary output enabled	1 = Single shot 0 = use TR2 for run	0 Not used
16 bit capture Capture on one edge only	0	0	01 = Capture on rising edge 10 = Capture on falling edge	0 Not used	0 Not used	Gating level on primary pin 0 = low 1 = high	0 Not used	1 = Gating enabled 0 = Gating disabled	1 = Single shot 0 = use TR2 for run	Capture and reload 0 = off 1 = on
16 bit capture Capture on both edges, no reload	0	0	11 = Capture on both eges	0 Not used	0 Not used	Gating level on primary pin 0 = low 1 = high	0 Not used	1 = Gating enabled 0 = Gating disabled	1 = Single shot 0 = use TR2 for run	0 = Capture and reload off
16 bit capture Capture on both edges, reload on both	0	0	11 = Capture on both edges	0 Not used	0 Not used	Start/stop edge 0 = start/stop on rising 1 = start/stop on falling	0 Not used	0 = reload on all edges	1 = Single shot T2POL[0] defines start/stop edge 0 = use TR2 for run	1 = Capture and reload on
16 bit capture Capture on both edges, reload on one edge	0	0	11 = Capture on both edges	0 Not used	0 Not used	Non reload edge and start/stop edge 0 = falling (start/stop on rising) 1 = rising (start/stop on falling)	0 Not used	1 = reload on one edge only T2POL[0] defines capture only edge	1 = Single shot T2POL[0] defines start/stop edge 0 = use TR2 for run	1 = Capture and reload on
16 bit counter	0	1	01 = rising 10 = falling 11 = both 00 = none (Not Used)	0 Not used Primary pin is input only	0 = secondary output not enabled 1 = secondary output enabled	0 Not used Primary pin is input only	Defines initial polarity of secondary output 0 = low 1 = high	0 Not used Do not set to 1	0 Not used Do not set to 1	0 Not used
Dual 8 bit compare with gating	1	0	00	0 = primary output not enabled	Secondary counter output enable 0 = not enabled 1 = output enabled	Defines gating level 0 = low 1 = high	Defines initial polarity of secondary counter outpu 0 = low 1 = high	0 = no gating 1 = gating enabled on primary pin	0 Not used	0 Not used
Dual 8 bit compare with no gating	1	0	00	1 = primary output enabled	Secondary counter output enable 0 = not enabled 1 = output enabled	Defines initial polarity of primary output 0 = low 1 = high	Defines initial polarity of secondary counter output 0 = low 1 = high	0 Not usable with primary output enabled	1 = Single shot 0 = use TR2 Only applies to primary counter	0 Not used
8 bit capture + 8 bit compare	1	0	01, 10, 11 The primary counter acts just as in 16 bit mode (except with only 8 bit resolution)	See 16 bit capture modes	Secondary counter output enable 0 = not enabled 1 = output enabled	See 16 bit capture modes	Defines initial polarity of secondary counter output 0 = low 1 = high	See 16 bit capture modes	See 16 bit capture modes	See 16 bit capture modes
8 bit counter + 8 bit compare	1	1	01 = rising 10 = falling 11 = both 00 = none (Not Used)	0 Not used Primary pin is input only	Secondary counter output enable 0 = not enabled 1 = output enabled	0 Not used Primary pin is input only	Defines initial polarity of secondary counter output 0 = low 1 = high	0 Not used Do not set to 1	0 Not used Do not set to 1	0 Not used

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