Comparator mode testing

ozpropdevozpropdev Posts: 2,490
edited 2018-12-08 - 11:29:00 in Propeller 2
Chip
I've been testing the comparator modes in P2 and I have a question.

PinA mode test.
A test ramp is fed into PinA(#8). I then read the INx for the pin
and output the comparator state to anoher pin(#16). This works fine.
Here's the scope capture
PinA_modes.PNG

PinB mode test.
Further tests put the ramp into PinB(#9) with PinA(#8) set for output.
The comparator state is also read from INx and output to pin #16.
This also wotks fine for both %1110 and %1111 modes.
Here's the two scope captures.
PinB_mode_1110.PNG
PinB_mode_1111.PNG

My question is the Pad IO table shows options for PinA output while PinA is used
as the comparator input. This seems to be a invalid configuration.
Am I missing something here?
Pad IO modes

M[12:0]		Input		PinA Output	CIOHHHLLL	OE	DAC	ADC	ADC mode	COMP
=============================================================================================================
1100_CDDDDDDDD	PinA > D	Out,1k5		C00001001	Dir	0	0	-		A>D
1101_CDDDDDDDD	PinA > D	!Input,1k5	C01001001	DIR	0	0	-		A>D
1110_CDDDDDDDD	PinB > D	Input,1k5	C00001001	DIR	0	0	-		B>D
1111_CDDDDDDDD	PinB > D	!Input,1k5	C01001001	DIR	0	0	-		B>D
=============================================================================================================
Here's my PinB test code
'%1111 mode (PinB > D, !Input)

dat		org

		wrpin	dacmode,#4		'ref out
		dirh	#4

		setbyte	compmode,#$df,#1	'threshold
		wrpin	compmode,#8
		dirh	#8
	
		rep	@loop,#0
		add	pa,#1
		setbyte	dacmode,pa,#1
		wrpin dacmode,#4		'set dac value
		testp	#8 wz
		drvz	#16			'comparator state
loop

dacmode		long	%0000_0000_000_10100_00000000_00_00000_0

compmode	long	%0000_0000_000_1111_000000000_00_00000_0

Melbourne, Australia

Comments

  • Here's my write up of the comparator config. I've tried to clarify the driving detail for each line in the config. In all cases there is a 1k5 series resister in the loop:
    	%11_VV_CDDDDDDDD = COMP_DAC comparator mode
    		DIR enables PinA digital output
    		%VV = Comparator config
    			00: IN = PinA > D, PinA driven by 1k5R from OUT
    			01: IN = PinA > D, PinA driven by 1k5R from !IN
    			10: IN = PinB > D, PinA driven by 1k5R from IN
    			11: IN = PinB > D, PinA driven by 1k5R from !IN
    		%DDDDDDDD = DAC level for internal analogue compare
    
    "There's no huge amount of massive material
    hidden in the rings that we can't see,
    the rings are almost pure ice."
  • Here's all the pad IO config write up I did - https://forums.parallax.com/discussion/comment/1452036/#Comment_1452036

    There is still a few question marks but I think I got most of the goodies in order. :)

    "There's no huge amount of massive material
    hidden in the rings that we can't see,
    the rings are almost pure ice."
  • evanhevanh Posts: 6,979
    edited 2018-12-08 - 15:02:50
    If you don't won't any feedback drive then use %00 and leave DIR low.

    "There's no huge amount of massive material
    hidden in the rings that we can't see,
    the rings are almost pure ice."
  • Mode 1101_CDDDDDDDD causes PinA to seek the internal comparator DAC level. With C=1, you can quantize what feedback is required to keep PinA at the DAC level.
  • cgraceycgracey Posts: 11,064
    edited 2018-12-08 - 16:44:19
    The !IN negative feedback modes are for driving a pin to the internal DAC level. With C=1, you get to quantize the feedback required to do so.

    The IN positive feedback mode %1110_CDDDDDDDD allows non-inverted feedback for using a transistor base or FET gate as the feedback delivery.
  • jmgjmg Posts: 13,469
    Sounds good.
    What is the speed of this mode ?
    What is the common mode voltage range ?
    A common spec point is to test 100mV overdrive tpd delays.
    Vos is not going to be easy to measure - maybe drive to 0 & Vio, and feed a scaled variable supply to find vos.
    Eg 1k & 10 ohms is 10mV/V

    I think there is no/minimal hysteresis in this mode ?
  • jmg wrote: »
    Sounds good.
    What is the speed of this mode ?
    What is the common mode voltage range ?
    A common spec point is to test 100mV overdrive tpd delays.
    Vos is not going to be easy to measure - maybe drive to 0 & Vio, and feed a scaled variable supply to find vos.
    Eg 1k & 10 ohms is 10mV/V

    I think there is no/minimal hysteresis in this mode ?

    It goes beyond the rails and has no intended hysteresis.
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