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efficient programming of ports partly in use

 
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jwolf

Bascom Member



Joined: 18 Jan 2013
Posts: 24
PostPosted: Tue Oct 20, 2015 7:17 pm    Post subject: efficient programming of ports partly in use Reply with quote
Dear forum community,
I have the following problem:
I need for controlling a dot matrix LED display 4 bits of one port (e.g. PC0 .. PC3 of an Atmega Cool ,
whereas other bits of the port (PC4 and PC5) are already in use for I2C.
For the output to PC0 to PC3 I just need to output a number 0 .. 7.
So what I coded looks like:
Code:
I = Row And &B00000100                                   'filter out rowadr bit 2
   If I = 4 Then
      Rowadr2 = 1
      Else
      Rowadr2 = 0
   End If
   I = Row And &B00000010                                   'filter out rowadr bit 1
   If I = 2 Then
      Rowadr1 = 1
      Else
      Rowadr1 = 0
   End If
   I = Row And &B00000001                                   'filter out rowadr bit 0
   If I = 1 Then
      Rowadr0 = 1
      Else
      Rowadr0 = 0
   End If


1st question: is there any other and more effective way to set the port bits (Rowadr0 .. Rowadr2)?

2nd question: I tried to program the same as expressed in the If Then Else statement using logic AND operations only,
but I was very surprised that the execution took longer !? (measuring the time between the output of subsequent Row addresses with the scope).

Any ideas?

(BASCOM-AVR version : 2.0.7.8 )
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MWS

Bascom Member



Joined: 22 Aug 2009
Posts: 2262

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PostPosted: Tue Oct 20, 2015 7:41 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
jwolf wrote:
For the output to PC0 to PC3 I just need to output a number 0 .. 7.

I do not see use of the 4th bit, 0-7 needs only 3 bits.
Also it is not clear from this chunk of code, where Rowadr0 starts, is it PC0?
If yes and in case "Row" will only contain values 0-7, your whole code can be replaced by:
Code:
I = PORTC AND &h11111000
PORTC = I OR Row
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jwolf

Bascom Member



Joined: 18 Jan 2013
Posts: 24
PostPosted: Tue Oct 20, 2015 8:20 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
Thank you for the reply,

sorry, I mixed up 1 .. 3 with 0 .. 2 - so of course 3 bits are sufficient to code 0 .. 7.
Your understanding is fully correct, Rowadr0 refers to port bit PC0.
I am aware of the possibility to write the entire port, but my fear was what would happen if I write to port bits that are used for other purposes and e.g. used as input?
So far I thought writing a 1 to a port bit that is configured as input would switch on the pull-up resistor?
Or is it only if I write the 1 to the port bit and when writing the entire port nothing would happen to the ports bits configured as input?

Best regards,
Johannes
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MWS

Bascom Member



Joined: 22 Aug 2009
Posts: 2262

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PostPosted: Tue Oct 20, 2015 8:31 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
jwolf wrote:
Your understanding is fully correct, Rowadr0 refers to port bit PC0.

Then my code fits.
Quote:
So far I thought writing a 1 to a port bit that is configured as input would switch on the pull-up resistor?

An AND of &h11111000 with, for example bit 7 (input, no pullup, so content 0), still gives 0, so no modifications done.
Reading a bit with 0 and writing it to 0 doesn't change anything.
Quote:
Or is it only if I write the 1 to the port bit and when writing the entire port nothing would happen to the ports bits configured as input?

There's one risk: if interrupts write to the same port, then my short code needs to be made atomar, which means encapsulated by a Disable/Enable Interrupts.
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olhexy

Bascom Member



Joined: 03 Apr 2011
Posts: 192
Location: Tilburg, Netherlands
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PostPosted: Tue Oct 20, 2015 9:08 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
jwolf wrote:
Dear forum community,
I have the following problem:
I need for controlling a dot matrix LED display 4 bits of one port (e.g. PC0 .. PC3 of an Atmega Cool ,
whereas other bits of the port (PC4 and PC5) are already in use for I2C.

Any ideas?

(BASCOM-AVR version : 2.0.7.8 )

Code:
 'By specifying Wr the library lcd4busy_anypin (based on LUCIANO) will be used
Config Lcdpin = Pin , Db4 = Portc.4 , Db5 = Portc.5 , Db6 = Portc.6 , Db7 = Portc.7 , E = Portc.2 , Wr = Portc.1 , Rs = Portc.0


Did you know that you can connect the LCDpins to every Port.bit as you wish?
For example:
Code:
Config Lcdpin = Pin , Db4 = Porta.4 , Db5 = Portb.5 , Db6 = Portc.6 , Db7 = Portd.7 , E = Portc.1 , Wr = Portb.2 , Rs = Porta.7

I am not sure if this goes for all versions of Bascom LCDlibraries, but if you do specify Wr, then you get lcd4busy_anypin Very Happy
Wr is in many older Bascom examples connected to ground, not to a Port.

Edit: My comment is for a HD44780 LCDdisplay. May be that a LEDdot display is totally different.

Last edited by olhexy on Tue Oct 20, 2015 9:40 pm; edited 1 time in total
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jwolf

Bascom Member



Joined: 18 Jan 2013
Posts: 24
PostPosted: Tue Oct 20, 2015 9:40 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
Thank you very much again.
This should solve my problem.
I will re-write my program accordingly and test it.

Best regards,
Johannes
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jwolf

Bascom Member



Joined: 18 Jan 2013
Posts: 24
PostPosted: Tue Oct 20, 2015 9:50 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
Dear olhexy,

I am not using a LCD display and thus not using any Bascom LCD library,
what I have is a LED dotmatrix with some logic inside which I need to control on low level, selecting lines and writing character patterns digit per digit.
I was also using LCD displays and the related library from Bascom, but was not aware so far of the Wr.
How can you specify Wr then?

Cheers,
Johannes
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olhexy

Bascom Member



Joined: 03 Apr 2011
Posts: 192
Location: Tilburg, Netherlands
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PostPosted: Tue Oct 20, 2015 10:20 pm    Post subject: Re: efficient programming of ports partly in use Reply with quote
jwolf wrote:

How can you specify Wr then?

You can just not mention Wr, or comment it out in de config
Code:
'Wr = ....
, then it is not specified.
(But then Wr must be connected to GND, or you can also connect to a Port.bit that you set low. With this setting you can only write, reading is not possible. No big problem, because reading LCD is rare. But it (Wr = 1) is needed for reading the Busyflag. In LCDdocs Wr is the same as R/W; it is usually pin 5 at LCDconnection)



If you bring it up in the Config, like
Code:
Wr = Portb.1
then it is specified. Simple!
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