Drive 33 Servos With One PIC + USART - Page 3 - Electronic Circuits Projects Diagrams Free

Pommie · 16th December 2007, 12:07 PM

I used a trick to get the serial working. I only check the serial if the count has bit 2 set. This gives a worst case scenario between serial checks of 3*4*8 = 96 cycles where each servo is 3 periods apart.

Here's the ISR code for the 8 cycle routine. It's not well commented but you should be able to follow it. Note, this hasn't even been assembled and definitely not tested!

Code:

		movlw	ServoBuffer
		movwf	FSR
		movlw	0xff
		movwf	PORTA		;0   set all on.
Wait		btfsc	INDF,2		;1/2 it set then we have 32 cycles to read serial and test for exit
		goto	DoSerial	;3   exit on 3
		incf	FSR,F		;3
		movfw	INDF		;4   prefetch port value
		decf	FSR,F		;5
Enter		decfsz	INDF,F		;6/7
		goto	Wait		;8
		movwf	PORTA		;8
		movlw	3		;0
		addwf	FSR,F		;1   point to next port value
		movfw	INDF		;2   prefetch incase time = 1
		decf	FSR,F		;3   back to time count
		goto	Enter		;5

DoSerial	movfw	FSR		;4   save the pointer
		movwf	FSRtemp		;5
		decf	FSR,F		;6   point to last port value
		movfw	INDF		;7   get it
		btfsc	STATUS,Z	;8/9 if it was zero, were done
		goto	Done		;    exit on 10
		btfss	PIR1,RCIF	;10/11
		goto	NoSerial	;    exit on 12
		incf	FifoStart,W	;14  get fifostart + 1
		andlw	FifoLength-1	;15  make it circular
		movwf	FifoStart	;16  
		addlw	FifoBuffer	;17  add start of buffer
		movwf	FSR		;18  put in indirect pointer
		movfw	RCREG		;19  get the received byte
		movwf	INDF		;20  put it in fifo
		movfw	FSRtemp		;21  restore the pointer
		movwf	FSR		;22
		decf	INDF,F		;23 - 8 = 15  reclaim 8 cycles
		decf	INDF,F		;15 - 8 = 7   and again
		decf	INDF,F		;7 - 8 = 2    and again
		nop			;3
		goto	Enter		;5

NoSerial	movfw	FSRtemp		;11  restore pointer
		movwf	FSR		;12
		decf	INDF,F		;13 - 8 = 5  reclaim 8 cycles
		goto	$+1		;7
		goto	$+1		;9
		decf	INDF,F		;9 - 8 = 1   and again
		goto	$+1		;3
		goto	Enter		;5

Mike.
Merry Christmas.

Edit, it also doesn't have the initial delay etc.

Mike, K8LH · 16th December 2007, 05:34 PM

So then, that must be the 8 MHz code with 4 usec 'step' size. Oh boy, I'm looking forward to studying it. At first glance it seems we're trying similar methods using counters...

That 16 MHz 1 usec 'step' code I was contemplating was an "unrolled" loop but I forgot about caching serial data. Oh well...

Code:

T1      movf    Val_01,W        ;
        decfsz  Tmr_01,F        ;
        goto    T1              ;
        xorwf   PORTB,F         ;
T2      movf    Val_02,W        ;
        decfsz  Tmr_02,F        ;
        goto    T2              ;
        xorwf   PORTB,F         ;
T3      movf    Val_03,W        ;
        decfsz  Tmr_03,F        ;
        goto    T3              ;
        xorwf   PORTB,F         ;
T4      movf    Val_04,W        ;
        decfsz  Tmr_04,F        ;
        goto    T4              ;
        xorwf   PORTB,F         ;

wschroeder · 17th December 2007, 03:39 AM

Since Mike K8LH has helped me think a little differently in my approach to code problems by judiciously using the abundance of PIC18 RAM to great advantage in developing his hirez servo positions, I think it's time to push the envelope with ROM when it comes to PIC16. Also note that controlling 33 servos from a PIC16 might only be possible from something like the new 16F887 running with its internal oscillator, which maxes at 8 MHz.

Here's my conceptual approach without having done any work yet on the problem, and it may provide some fodder for good minds. I once considered puttting a RETURN instruction at the last address of ROM and then calling various ROM addresses a given number of addresses before the RETURN instruction to create virtual delays, that is, delays that did not require any code or code loops. This is because when a PIC's ROM is cleared it becomes a nice series of NOP's, or single cycle instructions. This should work as long as you know how much ROM is left at the end of your MCU.

Imagine putting a RETURN instruction at the last address of the '887, or least at a known address. Since the servo period of 0 to 2500us is essentially a delay, it should be possible to make a Call to an address the number of addresses before the RETURN to create the necessary time delay.

A PIC16 will only allow 8 Calls since this is the maximum of the Stack. But over 20ms all 33 servos might get handled.

What do you think?

Mike, K8LH · 18th December 2007, 02:31 PM

That's certainly a good concept for a delay routine but I'm not sure how you'd use it for a 16F' servo controller where we're really trying to do a lot in just a few cycles (over and over again).

Regards, Happy Holidays, Mike

Mike, K8LH · 18th December 2007, 02:35 PM

How about a Servo-64 solution using a 28 pin 18F2620 and eight 74HC238 decoder IC's? It's an off-shoot from the 2.5 Kb buffer K8LH Soft-32 controller 'method'. It just won't support digital "on/off" outputs but I'm brain-storming a way to fix that using a latch or flip-flop IC instead of the decoder IC.

Happy Holidays everyone...

wschroeder · 18th December 2007, 04:18 PM

Hi Mike,

Yes, you're probably right... it was an idea that popped into my head.... not necessarily a good one.

wschroeder · 20th December 2007, 05:37 AM

I have not been treated more badly by any other forum administrator/moderator than this one...whoever it is doing this. In fact, I have never been banned from any forum, save this one. Passing notes publicly in the signature of my postings is possibly the worst form of decorum for someone in charge. I have email.

**Nigel Goodwin** · 20th December 2007, 10:23 AM

OK, quite simple answer - I responded in the same way you did - you made your point, I made mine in exactly the same way. If you had contacted me privately then I'd have responded privately.

I'll repeat again for you - if you want to advertise your commercial site please contact the administrator about advertising rates!.

Mike, K8LH · 21st December 2007, 01:49 AM

Nigel,

I must say I'm shocked to think that someone could possibly try and rationalize attaching those messages to someone elses posts. That must be the tackiest thing I've witnessed here.

May I ask if there's an authority, other than you, with whom I could lodge a complaint?

Sincerely,

Michael McLaren, K8LH

Pommie · 21st December 2007, 09:02 AM

I also think that Warren's treatment is a little harsh. Considering he has only 55 posts, his contributions are very informative.

Mike.

yanny_boy · 14th July 2008, 03:23 PM

Is there a nice simple circuit for the 18f4550 that I can use with schroeders code? This is perfect as I need to drive 20 servos...... any suggestions would be great... thanks.

threewire · 21st October 2008, 10:39 AM

Quote:

Originally Posted by wschroeder

Dear wschroeder,

You wrote an awesome code for 18F452.I am thinking of making a servo controller for my project.Could you please post the circuit diagram and the control protocol for controlling the servos from th serial port.I have experience in programming AVR but I am totally new to PIC.

Hoping for a positive reply.

Ubergeek63 · 21st October 2008, 03:13 PM

ok, I don't get it... why aren't you just using a counter, interrupt driven serial routine (three byte min block - table addy, byte count, data ), and an endless loop?

Pommie · 21st October 2008, 03:22 PM

Quote:

Originally Posted by Ubergeek63

ok, I don't get it... why aren't you just using a counter, interrupt driven serial routine (three byte min block - table addy, byte count, data ), and an endless loop?

Was there a particular post you were replying to?

Mike.

Ubergeek63 · 21st October 2008, 05:18 PM

Quote:

Originally Posted by Pommie

Was there a particular post you were replying to?

Mike.

No, just a very quick scan of the posts. With and interrupt routine repsonding UART to update the desired PWM values, a simple endless loop looks up the value and compares it to a time counter to reset it's pin and they all get set on the overflow interrupt.

It stalls briefly on serial reception, but that is easier to deal with than having to make time for 30 bytes regularly...

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16th December 2007, 05:34 PM	(permalink)
Mike, K8LH	So then, that must be the 8 MHz code with 4 usec 'step' size. Oh boy, I'm looking forward to studying it. At first glance it seems we're trying similar methods using counters... That 16 MHz 1 usec 'step' code I was contemplating was an "unrolled" loop but I forgot about caching serial data. Oh well... Code: T1 movf Val_01,W ; decfsz Tmr_01,F ; goto T1 ; xorwf PORTB,F ; T2 movf Val_02,W ; decfsz Tmr_02,F ; goto T2 ; xorwf PORTB,F ; T3 movf Val_03,W ; decfsz Tmr_03,F ; goto T3 ; xorwf PORTB,F ; T4 movf Val_04,W ; decfsz Tmr_04,F ; goto T4 ; xorwf PORTB,F ; Last edited by Mike, K8LH; 16th December 2007 at 05:43 PM.

17th December 2007, 03:39 AM	(permalink)
wschroeder	Since Mike K8LH has helped me think a little differently in my approach to code problems by judiciously using the abundance of PIC18 RAM to great advantage in developing his hirez servo positions, I think it's time to push the envelope with ROM when it comes to PIC16. Also note that controlling 33 servos from a PIC16 might only be possible from something like the new 16F887 running with its internal oscillator, which maxes at 8 MHz. Here's my conceptual approach without having done any work yet on the problem, and it may provide some fodder for good minds. I once considered puttting a RETURN instruction at the last address of ROM and then calling various ROM addresses a given number of addresses before the RETURN instruction to create virtual delays, that is, delays that did not require any code or code loops. This is because when a PIC's ROM is cleared it becomes a nice series of NOP's, or single cycle instructions. This should work as long as you know how much ROM is left at the end of your MCU. Imagine putting a RETURN instruction at the last address of the '887, or least at a known address. Since the servo period of 0 to 2500us is essentially a delay, it should be possible to make a Call to an address the number of addresses before the RETURN to create the necessary time delay. A PIC16 will only allow 8 Calls since this is the maximum of the Stack. But over 20ms all 33 servos might get handled. What do you think? Last edited by wschroeder; 17th December 2007 at 03:41 AM.

18th December 2007, 02:31 PM	(permalink)
Mike, K8LH	That's certainly a good concept for a delay routine but I'm not sure how you'd use it for a 16F' servo controller where we're really trying to do a lot in just a few cycles (over and over again). Regards, Happy Holidays, Mike

18th December 2007, 02:35 PM	(permalink)
Mike, K8LH	How about a Servo-64 solution using a 28 pin 18F2620 and eight 74HC238 decoder IC's? It's an off-shoot from the 2.5 Kb buffer K8LH Soft-32 controller 'method'. It just won't support digital "on/off" outputs but I'm brain-storming a way to fix that using a latch or flip-flop IC instead of the decoder IC. Happy Holidays everyone...

18th December 2007, 04:18 PM	(permalink)
wschroeder	Hi Mike, Yes, you're probably right... it was an idea that popped into my head.... not necessarily a good one. Last edited by wschroeder; 18th December 2007 at 04:32 PM.

20th December 2007, 05:37 AM	(permalink)
wschroeder	I have not been treated more badly by any other forum administrator/moderator than this one...whoever it is doing this. In fact, I have never been banned from any forum, save this one. Passing notes publicly in the signature of my postings is possibly the worst form of decorum for someone in charge. I have email.

20th December 2007, 10:23 AM	(permalink)
Nigel Goodwin	OK, quite simple answer - I responded in the same way you did - you made your point, I made mine in exactly the same way. If you had contacted me privately then I'd have responded privately. I'll repeat again for you - if you want to advertise your commercial site please contact the administrator about advertising rates!. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

21st December 2007, 01:49 AM	(permalink)
Mike, K8LH	Nigel, I must say I'm shocked to think that someone could possibly try and rationalize attaching those messages to someone elses posts. That must be the tackiest thing I've witnessed here. May I ask if there's an authority, other than you, with whom I could lodge a complaint? Sincerely, Michael McLaren, K8LH

21st December 2007, 09:02 AM	(permalink)
Pommie	I also think that Warren's treatment is a little harsh. Considering he has only 55 posts, his contributions are very informative. Mike.

14th July 2008, 03:23 PM	(permalink)
yanny_boy	Is there a nice simple circuit for the 18f4550 that I can use with schroeders code? This is perfect as I need to drive 20 servos...... any suggestions would be great... thanks.

21st October 2008, 03:13 PM	(permalink)
Ubergeek63	ok, I don't get it... why aren't you just using a counter, interrupt driven serial routine (three byte min block - table addy, byte count, data ), and an endless loop?