FORCE_HW & FORCE_SW

msa · Joined: 07 Apr 2010 Posts: 15

Hi all

What difference between FORCE_HW and FORCE_SW when use #USE I2C.

thanks

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The CCS manual says:

msa · Joined: 07 Apr 2010 Posts: 15

Thank you for your answer.

with regards

tim_sid · Joined: 11 Apr 2014 Posts: 16

so, for software I2C is simple ccs I2C_read() and I2c_write functions are enough or I need to use some library performing some bit banging? can I have some simple code or clue, Please?

oxo · Joined: 13 Nov 2012 Posts: 219 Location: France

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Just one additional note: You didn't mention if you want to use it on a master or on a slave device. Software I2C on a master works great but don't try to use it on a slave.

tim_sid · Joined: 11 Apr 2014 Posts: 16

Thank you so much for quick replies.
Ckielstra, I just need my PIC working in Master mode for writing to slave device.

RoGuE_StreaK · Joined: 02 Feb 2010 Posts: 73

Is it correct to say that hardware i2c (and PWM, and SPI etc) works independent of your other code, that once the command is given the hardware itself performs the task, freeing up the processor to do other things? Kind of like delegating a job to someone else, you can continue with more important tasks whilst they do the tedious repetitious stuff?

Ttelmah · Joined: 11 Mar 2010 Posts: 19266

Yes.

However for I2C the difference is normally tiny. At 100KHz, it only takes 80uSec to send a byte. Using software I2C won't normally reach this rate (except on a fast PIC), but the actual time to send a byte is still small.
Different from RS232 where byte times are often several mSec.

Best Wishes

jeremiah · Joined: 20 Jul 2010 Posts: 1320

Note that however, while hardware does work independently of software in general, you still have to consider driver and built in function implementations. Some of those will loop infinitely waiting for a hardware flag to set before moving on. For example, if you use putc or printf to print to a hardware UART, it will wait until the buffer has room before adding the next character to the outgoing buffer. Using getc will wait until there is a character before moving on.

You can get around these limitations in various ways:
1. Some peripherals have built in support functions or parameters for avoiding those delays
2. Some peripherals can be implemented using interrupts to get around this (usually with extra code from you)
3. You can write your own drivers or peripheral functions to use instead.