Mcp 23017 and Pic 16f877

[Demon]

Would a pull-down resistor at each LED solve the problem?

[CLAUDY]

In fact the Pcb is done simply for the moment to get used to the MCP23017 that will serve me to something else after.

The PCB is composed of 8 LED simply placed on Port A and 8 LED placed on port B. The communication with the Pic I2C is done.
Pic also controls an LCD 2 * 16.

The test program is to enable a counter from 1 to 255 that will be displayed on the LCD (i = 1 until i = 255) and the 2 * 8LED (port A and port B).

At the first power, while port A is activated (LED lit) and port B is disabled (LED off). When the counter reaches + / - 130 (viewed from the LCD), Port A (which was fully activated) starts from the port B but it does not change state. And only when the counter recomm early as 2 port (A and B) fonctionnnent normally (they have at the same time as the LCD).
And it works very well.
The problem is powering up.

The problem must come from the Start Bit of the I2C.
I already tried some codes for the Start bit but I can not.

Aurra you an idea?


Again thank you for your reply

Claudy

[Demon]

In fact the Pcb is done simply for the moment to get used to the MCP23017 that will serve me to something else after.
...

Are you saying the MCP23017 is NOT used at the moment? Why issue an I2C command to something inactive? Do you have LEDs connected on the MCP23017?

The PCB is composed of 8 LED simply placed on Port A and 8 LED placed on port B.
...

sda var porta.0 'sda est sur le porta.0
scl var porta.1 'scl est sur le porta.1

So you have 16 LEDs on ports A and B, but you also use Port A for I2C communication?

Why not use Port C.3 for SCL and Port C.4 for SDA (PIC 16F877 datasheet pinout p.3) to avoid interfering with your LEDs?

[mister_e]

Plus ça change, plus c'est pareil...

KeyWord: Datasheet

Not ALL PORTA pins are true output... and on PORTB there's this PGM pin who could do nasty thingy if your CONFIG FUSES aren't set properly...

About them (Config fuses) Where are they?!?

Are we talking about a 877 or 877A ?

And finnally... you want to manually assign value to your PORT BEFORE doing anything else... say BEFORE the PAUSE 1000. Usually

PORTA=0
PORTB=0
...
TRISA=0
TRISB=0
....
Variable and all other code here.

Bonne chance

[mister_e]

sda var porta.0 'sda est sur le porta.0
scl var porta.1 'scl est sur le porta.1

So you have 16 LEDs on ports A and B, but you also use Port A for I2C communication?

Why not use Port C.3 for SCL and Port C.4 for SDA (PIC 16F877 datasheet pinout p.3) to avoid interfering with your LEDs?

Actually If I understand properly, it is worst than this. If the LED are connected to Ground on the I2C line, they Screw-up the line as they have to be Pulled-high (hi-z) but the LED LOAD it to gnd.

Get rid of the LED on those I/O or, like BobyBert said, move the I2C line elsewhere (it doesn<t need to be on a specific SCL, SDA PIC line as you're using I2CREAD/I2CWRITE who's not using the built in SSP module). You want the I2C line on their own I/O.

[CLAUDY]

Hello,

Thank you for your answers.

When I speak of the port A and B have ports MCP23017 and not PIC.
The PIC used is a 877A.
The PIC controls only the LCD and I use the port A of the PIC to bond with the I2C MCP23017.

A big thank you for your help.

Soon

Claudy

[Acetronics2]

Hi, Claudy

Following your adventures on many forums for a moment ... I still miss a small thing : YOUR USED SCHEME ...

Alain

[CLAUDY]

Hello Alain,

I still have not found the solution.

Here's a quick diagram as requested.Printing TEST MCP23017-sch.pdf

Thank you

Claudy