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Dead-band delay PWM

 
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Eddy71ua



Joined: 23 Sep 2009
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Dead-band delay PWM
PostPosted: Wed Apr 14, 2021 12:45 am     Reply with quote

In Half-Bridge mode, a digitally programmable dead-band delay is available to avoid shoot-through current from destroying the bridge power switches.
What command can I use to set this time?
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Wed Apr 14, 2021 3:29 am     Reply with quote

You need to say 'what chip'.
There are about seven different actual PWM implementations on different
PIC's (some even have two different ones in a single chip), and the
settings for each are different.
temtronic



Joined: 01 Jul 2010
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PostPosted: Wed Apr 14, 2021 4:47 am     Reply with quote

Seven ? just seven ??
sigh...PICs are too complicated today !
Can we reset the clock back to the EASY days of the 16C84 please ? Very Happy

Bet uchip will announce an 8th PWM before this gets posted Laughing
Eddy71ua



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PostPosted: Wed Apr 14, 2021 5:31 am     Reply with quote

Ttelmah wrote:
You need to say 'what chip'.


Sorry. PIC16F1823
Register PWM1CON

I couldn't find the command, so I used this combination:

#byte PWM1CON = 0x294

...

PWM1CON = xx;
temtronic



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PostPosted: Wed Apr 14, 2021 6:40 am     Reply with quote

PWM1CON is an 8 bit register, so you can't actually, phyiscally make it 0x294.....
Ttelmah



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PostPosted: Wed Apr 14, 2021 7:40 am     Reply with quote

In which case this has the basic ECCP module.

Very simple. If you look at the manual, you will see that the setup_ccp1
function allows you to specify setup_ccp1(mode) or, setup_ccp1(mode, pwm).
The 'pwm' parameter here is the deadband time.

He is not setting PWM1CON to 0x294, that is it's address. However I would
say to always use the name instead of a physical address.

#byte PWM1CON = getenv("SFR:PWM1CON")

is safer, and much more informative than manually putting in addresses.

setup_ccp1(CCP_PWM_HALF_BRIDGE, 1);

Gives you one clock cycle of deadband delay.

Assembles as:
Code:

....................    setup_ccp1(CCP_PWM_HALF_BRIDGE, 1);   while(TRUE)
000B:  MOVLB  01
000C:  BSF    TRISC.5
000D:  MOVLB  05
000E:  CLRF   CCP1CON
000F:  MOVLW  80
0010:  MOVWF  CCP1CON
0011:  MOVLW  01
0012:  MOVWF  PWM1CON //you see the '1' put in here
0013:  CLRF   CCP1AS
0014:  MOVWF  PSTR1CON


The manual does tell you this:
Quote:

pwm parameter - is an optional parameter for chips that includes ECCP module. This parameter allows setting the shutdown time. The value may be 0-255.


Though they for some reason call it shutdown time, rather than deadband.
Eddy71ua



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PostPosted: Wed Apr 14, 2021 8:04 am     Reply with quote

Thank you Ttelmah.

I'll be experimenting.

Code:
setup_ccp1(CCP_PWM_HALF_BRIDGE, 1);


The command does not work - the PWM output is zero.

Code:
setup_ccp1(CCP_PWM|CCP_PWM_HALF_BRIDGE, 1);


This design works fine.

Smile
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