I/O extender

[mychangl]

Happy New Year to all....

Currently, i am still using pic16f84a for my project due to smaller size and no special task require. However the only problem is limited I/O. I also plan to migrate to pic16f628 soon. I/O still a problem for me. I have gone through some article to expand I/O however it is very limited. Is there any way to increase it to 32 or 64 ? How ?

Thx..

[mackrackit]

It depends on what you want to do with the I/Os.

An RC network using the ADC or POT or RCTIME for inputs.

Outputs could be a "matrix" http://www.mackrackit.com/mac/www/dave/LED/LEDs.html

But shift registers are I think the best, they can be used for both in and out. Three pins from the PIC can be turned into eight outputs. Four pins can be turned into 16 outputs by sharing the clock an load pins on the registers.

Example for reading one register.

Clock   var PORTB.7

Load    var PORTB.6

Data_1  var PORTB.5

pulsout Load,1

shiftin Data_1,Clock,MSBPre,[keys]

[Luciano]

Hi,

See the Microchip MCP23016. (16-bit bidirectional I/O port expander).

You can address up to eight MCP23016 in your system so this
will give you up to 128 I/O pins.

Microchip MCP23016 16-Bit I2C™ I/O Expander
http://ww1.microchip.com/downloads/e...Doc/20090b.pdf

Interfacing The MCP23016 I/O Expander with the PIC16F877A:
http://ww1.microchip.com/downloads/e...tes/00245a.pdf


* * *

There is also a version with an 8-bit bidirectional I/O port.

Microchip MCP23008 8-Bit I/O Expander with I2C Interface
http://ww1.microchip.com/downloads/e...Doc/21919e.pdf

Best regards,

Luciano

[mychangl]

Thx Mackrackit.
It only High and Low I/O. i think shift register would be a good idea. 4 to 8 lines. Bringing total of 128 bit of I/O. Meaning total pin require is 7 ( 4 for address, Clock, Load and Serial Data ). Am i right ?

Thx Luciano for the suggestion. It really a new thing for me. But why both MCP23008 and MCP23016 have 3 addresses ? Can MCP23016 work with 16f84a ?

[Luciano]

Thx Luciano for the suggestion. It really a new thing for me.
But why both MCP23008 and MCP23016 have 3 addresses ?
Can MCP23016 work with 16f84a ?

Hi,

With three address lines you can set the address of up to eight devices.

Binary / Decimal 
============
000   =   0
001   =   1
010   =   2
011   =   3
100   =   4
101   =   5
110   =   6
111   =   7

The MCP23016 will work with the 16f84a.
Use the software I2C commands of PicBasic Pro. (I2CIN and I2COUT).

* * *

See also this: (Basic Stamp + MCP23016).
http://www.parallax.com/dl/docs/cols.../col/nv109.pdf

Best regards,

Luciano

[mychangl]

Use the software I2C commands of PicBasic Pro. (I2CIN and I2COUT).

Do you mean I2Read and I2Write ?
Sorry i am not familiar with it. However i would like to try.

Correct me if i am wrong.
From datasheet,
control 0h and 1h is to read or write to the ports
control 6h and 7h is to set port as input or output

Given scenario 1 :
Connect 23016 address as $01
Assign GP0.0 to GP0.7 as input (control address is 6h)
Assign GP1.0 to GP1.7 as output (control address is 7h)

the code will be :
addr var byte
addr=01
I2CWRITE DataPin,ClockPin,06,addr,[FF]
I2CWRITE DataPin,ClockPin,07,addr,[00]

Scenario 2 :
Read the data on GP0.0 to GP0.7 and put inside Sample1

the code will be :
I2CREAD DataPin,ClockPin,00,addr,[Sample1]

Scenario 3 :
Write data 44h on GP1.0 to GP1.7

the code will be :
I2CWRITE DataPin,ClockPin,00,addr,[44]

[mackrackit]

Thx Mackrackit.
It only High and Low I/O. i think shift register would be a good idea. 4 to 8 lines. Bringing total of 128 bit of I/O. Meaning total pin require is 7 ( 4 for address, Clock, Load and Serial Data ). Am i right ?

Thx Luciano for the suggestion. It really a new thing for me. But why both MCP23008 and MCP23016 have 3 addresses ? Can MCP23016 work with 16f84a ?

If you go with shift registers you will need a clock/load set for inputs and one for outputs.
Look at a HC595 for output and HC165 for inputs (I think, been awhile)

The solution that Luciano gave looks nice. I did not know about these chips. Learned something new and it is the fisrt day of the year Off to a good start.

[mister_e]

Those microchip I/O extender are really nice. In the past i also used PCF8574A, maybe easier to find it locally 'cause it's a very old one.. still popular i guess.

[ronjodu]

I use 3 of the Maxim Max6957's for a total of 60 additional I/O's with only 3 PIC pins thru SPI interface. They also have a I2C version. In my app. 52 are used for LED's and 8 will be used for relays. TFM is a bit intimidating at first. I could post some code if interested.

Hope this helps.

!!!!!!!!!!!! Happy New Year to All !!!!!!!!!!!!!!

[mychangl]

Interesting. If it is feasible, why not. However I just checked with our local distributor and they do not have max6957. Perhaps i should keep looking for the availability. I keep that in mind. Thx Ronjodu