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I2c non blocking



Author: Dany

Last Updated: 2015-07-08

Category: Internal MCU modules

Downloaded: 2138 times

Followed by: 5 users

Replacement routines for I2c1_Rd and I2c1_Wr but here with timeout, so no blocking any more when a device one tries to access is not present.
The mE I2c library is still needed for the remaining I2c routines.

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Library Blog

Library I2c_TimeOut

This library contains replacements for I2c1_Rd and I2c1_Wr with timeout functionality (so non blocking).
For the moment only available for P16 and P18 PIC's with only one HW I2c module.

All other routines of mE's I2c library are not replaced, and have to be used as before.

The interface of the non blocking (with TimeOut) I2c routines library is:
// interface

function I2C1_Rd_TimeOut(Ack: byte; TimeOut: word): byte;
// TimeOut should be >0 !  Its value is in units of 10us, so '50' means a timeout of '500 us'
// A timeout less than 100us (value of TimeOut = 10) is useless with 100 Khz clock speed.
// This function returns the I2c value read (except when I2c timeout, see below).
// See also the variables "I2c_TimeOut" and "I2C_LastError" below.

procedure I2C1_Wr_TimeOut(data_: byte; TimeOut: word);
// TimeOut should be >0 !  Its value is in units of 10us, so '50' means a timeout of '500 us'
// A timeout less than 100us (value of TimeOut = 10) is useless with 100 Khz clock speed.
// See also the variables "I2c_TimeOut" and "I2C_LastError" below.

var I2c_TimeOut: word; // After using one of the above routines the remaining timeout can be found in this variable.
                       // Check this value for an indication how close an I2C device comes to a timeout state.
    I2C_LastError: byte; // Gives the success or failiure state after using one of the above routines:
    // The following values can occur:
    //   _I2C_OK: NO error, all OK
    //   _I2C_TIMEOUT: TimeOut error
    //   _I2C_NO_ACK: No acknowledge from slave (writing only)
const // values for I2C_LastError
   _I2C_OK      = 0;
   _I2C_TIMEOUT = 1;
   _I2C_NO_ACK  = 2;


The outcome (success or some failiure) can be found in variable "I2C_LastError", see above for the possible values.
The routine usage is e.g.:
  I2c1_Wr_TimeOut(Data_, 250); // Write “Data_” with a timeout of 2500 microseconds (2.5 millisecs)
  // Check if there was a problem during above I2c write try:
  If (I2C_LastError = _I2C_OK)
  then ...                    // all OK
  else If (I2C_LastError = _I2C_TIMEOUT)                       
  then ...                    // timeout error, no response in time from the I2c device
  else If (I2C_LastError = _I2C_NO_ACK)
  then ...                    // no ack from the I2c device

If no errors occured then the time left over from the total timeOut value (in above example the "250") can be found in variable "I2c_TimeOut"

Normally an I2c transmission takes at least 90 microseconds at 100Khz, so a timeout value of less than 10 is useless.

Have fun!


2015-01-26: Replaced the mB files: all mB files are compilable now (which e.g. means that all "with" statements are dealt with). I could however not link and test the libraries (no mB licence).

Version 2.0, dd 2015-07-08: changed the interface of the library. Thanks Rainer Hantsch for the testing and  valuble suggestions!


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