In SX Microcontrollers, SX/B Compiler and SX-Key Tool, ponypat wrote:

Hi all,
 

I'm attempting to do some work with an access.bus accessory... which for purposes of discussion here, is pretty much the same interface electrically as I2C.

 

I developed a short program that would send some data out via I2C.  There's a section of code that goes something like this:

 

  LED=0
  I2CSTART SDA
  I2CSEND SDA, [i]byte1[/i]
  LED=1
  I2CSEND SDA, [i]byte2[/i]
  LED=0
  I2CSEND SDA, [i]byte3[/i]
  LED=1

[...]

 

Note that "LED" is now only being used as a trigger to the logic analyser, I was just too lazy to change the variable name.

 

LED is RB.7, and SDA is RA.0, putting SCL on RA.1.  All other pins are unused, and this is all on the eval board prototype area with the SX-key.  As per suggestion on the I2C example, both signals are pulled up via 4.7K resistors -- a bit stronger than I was originally using, but that's probably fine.

 

My questions are:

1) When I select Run -> Run to download and start the code, it takes about ~239uS to send 6 bytes, start to finish.  But when I reset it via the button, it takes 1.195ms to send the same bytes, start to finish.  Any reason why?

 

2) Is there any kind of more thorough docs on the I2C routines?  Specifically, is there any buffering while sending?  And if it attaches to a bus where there's an ongoing stream of data, will it eventually figure out a way to sync up and start sending ack bits, or does it require a START event? 

 

I see there's an i2c example in the Daubach book as well, so if I can decipher sx assembler, maybe I'll give that a try.

 

Anyway, thanks for any help!

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