Multiplexer channel selection

It's more of a conceptual question then a programming issue. I use a pic to control the inputs of a 16 channel multiplexer, thus allowing me to select a certain channel and read voltages from a multi cell battery pack. How do I inteligently cycle through the mux control inputs other then aliasing ports and attributing values ?

Code:

---

a_mux        var        porta.1
b_mux        var        porta.2
c_mux        var    porta.3
d_mux        var        porta.4
inh        var    porta.5

'select MUX channel X0
a_mux = 0:b_mux = 0:c_mux =        0:d_mux = 0:inh  = 0
'select MUX channel X1
a_mux = 1:b_mux = 0:c_mux =        0:d_mux = 0:inh  = 0
'select MUX channel X2
a_mux = 0:b_mux = 1:c_mux =        0:d_mux = 0:inh  = 0
'select MUX channel X3
a_mux = 1:b_mux = 1:c_mux =        0:d_mux = 0:inh  = 0
'and do this up to channel 15

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It would be really useful to cycle using a for.. next loop and I belive it's quite possible because the multiplexer's truth table consists of consecutive binary numbers for the selection inputs. I'm thinking something like:

Code:

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i var byte

a_mux        var        porta.1
b_mux        var        porta.2
c_mux        var    porta.3
d_mux        var        porta.4

i.7 var a_mux
i.6 var b_mux
i.5 var c_mux
i.4 var d_mux

for i= 0 to 15      ' meaning i=00000000
                                00000001
                                00000010

' do stuff
next i

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But it doesn't compile well because quote "Variable already an alias". How do I get around this ? All the code above is just for demo purposes, I know TRIS is not set and the other stuff that goes into an actual program is missing

Hello Castor,
I am not good at them,but I believe you are looking for an ARRAY.
see:http://www.picbasic.co.uk/forum/showthread.php?t=8486
http://www.google.com/custom?hl=en&c...picbasic.co.uk

hi,

your answer is "something like that"

... but as the PIC will perform the A/D conversion ... a Porta Analog input has some good chance to be in use ... if you do not use another ADC input ( PortE 0,1 or 2 for a 16F877a )


without any headaches ... it gives

Code:

---


Porta.5 = 0                ' Enable the Mpxer

for I = 0 to 15

 Porta =  (Porta & %11000001 ) + (I *2)  ' Keep Porta.5 low, Porta.0,6,7 as is, and Porta1-4 select the input
 Pause 5                              ' to stabilize Mpxer Output voltage
 ADCin Portx.y, value[I]          ' Portx.y is where the Mpxer output is connected ...
                                          'value[I] is the table location corresponding to the cell
NEXT I

.
.
.

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too simple !

Alain

PS: May be someone could explain me why writing [] with UPPERCASE I inside the brackets show

Code:

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[I]

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...

Quote:

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PS: May be someone could explain me why writing [] with UPPERCASE I inside the brackets show

Code:

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[I]

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...

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Italics vs. Italics

Italics vs. [ I ] Italics [ / I ]

http://www.phpbb.com/community/faq.php?mode=bbcode

Quote:

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Originally Posted by skimask

Italics vs. Italics

Italics vs. [ I ] Italics [ / I ]

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Hi, Ski

Yes ... Ok, But ALSO inside a CODE window ...???

could we talk about a BUGGGGGGGGG ????

Alain

Quote:

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Originally Posted by Acetronics

... but as the PIC will perform the A/D conversion ... a Porta Analog input has some good chance to be in use ... if you do not use another ADC input ( PortE 0,1 or 2 for a 16F877a )

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Hey, thanks for the great answer.
It works like a charm. In fact I use a 16 bit external A/D converter so using PORTA pins as digital I/O doesn't pose an issue. What if the selection pins are scattered across two ports ? Can I get around that without selecting each and every output manually ? Or reworking the board ? (I didn't quite think about channel selection when I built it) :)

Quote:

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'DCD
'----------
'RE2 G1,G2
'RB7 A
'RB6 B
'RB5 C
'RC6 D

---

Quote:

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Originally Posted by Castor

What if the selection pins are scattered across two ports ?

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Why not ...

you'll have to write two lines for Ports masking instead of one !

Quote:

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Can I get around that without selecting each and every output manually ? Or reworking the board ?

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if you have a pot or button available and a free Pic input or two ... you can easily make the manual channel selection "by soft" ...

Quote:

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(I didn't quite think about channel selection when I built it) :)

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but , may be, you'll have to add a small board on the existing one ( in french : une impériale !!! )

Alain

Quote:

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Originally Posted by Acetronics

Yes ... Ok, But ALSO inside a CODE window ...???
could we talk about a BUGGGGGGGGG ????

---

I don't know if it's a bug or not. Maybe bbCode doesn't handle nested tokens, or at least that nested token correctly, maybe it was intended to be that way.

Please stay on topic.

Here's a summary: I have two pesky devices in my circuit. A multiplexer and a decoder.The multiplexer is connected as:

Code:

---

MUX
'------------
'RA5        INH
'RA1        A
'RA2        B
'RA3        C
'RA4        D
'------------

---

notice how the selection channels are on consecutive pins thus making things easy for selecting the channels:

Code:

---

'mux channel selection
'low inh_mux
'for i= 0 to 15
'      Porta =  (Porta & %11000001 ) + (i *2)        'port masking for cycle purposes
'next i

---

On the other hand the decoder pins are scattered across PORT B and PORTC:

Code:

---

'DCD
'----------
'RE2        G1,G2       
'RB7        A
'RB6        B
'RB5        C
'RC6        D

---

here's the code i've devised:

Code:

---

'dcd channel selection
low g_dcd
for i=0 to 15
        portb = (portb & %00011111 ) + (i rev  3)<<5
        portc = (portc & %10111111 ) + (i<<3)
next i

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The PORTB pins selection works fine (meaning lines A, B and C of the decoder behave as I expected). But line D (the only one on PORTC) gives me a headache. Am I missing something in the mask ?

Quote:

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Originally Posted by Castor

Please stay on topic.

---

Guess what? Free help! Deal with it.

Code:

---

'dcd channel selection
low g_dcd
for i=0 to 15
        portb = (portb & %00011111 ) | ( ( i rev  3 ) << 5 )
        portc = (portc & %10111111 ) | ( i << 3 )
next i

---

OR don't ADD

Quote:

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Originally Posted by skimask

Guess what? Free help! Deal with it.

Code:

---

'dcd channel selection
low g_dcd

for i=0 to 15
        portb = (portb & %00011111 ) | ( ( i rev  3 ) << 5 )
        portc = (portc & %10111111 ) | ( i << 3 )
next i

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OR don't ADD

---

to get rid of the i lower bits for portC ...

i would have used

Code:

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portc = (portc & %10111111 ) | ( i.3 << 6 )

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but, it's me ...

Alain

Quote:

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Originally Posted by Acetronics

portc = (portc & %10111111 ) | ( i.3 << 6 )[/code]

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I've tried to do something like that before. If I remember right, the fact that i.3 is a bit didn't work well with the << 6. It ended up shifting itself out into nowhere and always ended up being a '0'.
Maybe that was back in the day, in an older version of PBP or something. It just seems to me like that didn't work very well.

Hi,

I did at test on the breadboard this morning ...

Everything fine ...

Alain

This is the winner:

Code:

---

portb = (portb & %00011111 ) | ( ( i rev  3 ) << 5 )
        portc = (portc & %10111111 ) | ( i.3 << 6 )

---

I've tried both in MPLAB SIM but

Code:

---

        portc = (portc & %10111111 ) | ( i << 3 )

---

doesn't mask the port right.

THANK YOU. Problem solved

Good news !

Just for the fun ...

How many boards saved ???

Alain

uhm .. one :)

I'll post the code in the apropriate section when it's done. It's for a Li-Ion Battery Management System (BMS)/Balancer

Hi, Castor

What is your device for ??? Modelling purposes ?

By the way, I realized a voltage warning device for transmitters ( for a Nicad to LiPo conversion ), some times ago, and, by the way noticed there's a not negligible tempco with those batts ...

doesn't simplify the measurements !!!

Regards from ... an ex Tegel " blue uniform " temporary citizen.

Alain

it's for an electric golf cart I'm building