you have to align this up to the clock speed of the processor. func i2c_delay_T2 delay 5.0 microsec with 4 Mhz crystal i2c_delay_T2: 4 cycles a nop delays 1 count. We can do that with “nop”s, and we’ll paste it below. For our example, we’ll simply put in 80 counts to delay 4 times as long. To get 100 kHz, Fleury has originally written for 20 counts to give a 5.0 microsecond delay. From the assembler page, we can see that the “nop” function delays 1 count or cycle. In our example, we’re using an external clock of 16 Mhz, 4 times as fast as the original program was written for. Modifying this section of the program is all about getting the counts correct. endfunc total 20 cyles = 5.0 microsec with 4 Mhz crystal func i2c_delay_T2 delay 5.0 microsec with 4 Mhz crystal i2c_delay_T2: 4 cycles rjmp 1f 2 “ 1: rjmp 2f 2 “ 2: rjmp 3f 2 “ 3: rjmp 4f 2 “ 4: rjmp 5f 2 “ 5: rjmp 6f 2 “ 6: nop 1 ” ret 3 ”.
#ATTINY85 PORT PINS ADDRESS CODE#
Let’s start with the original code below. We dug around and found some info on delays in AVR here, at least enough to help us modify the delay. However, some sensors require a both precise and accurate (for example many SMBus sensors require clocks speeds of less than or equal to 100kHz).įleury’s files are written in AVR Assembler, which is not an incredibly user-friendly or easy-to-use language. Because I2C is a 2-wire protocol, it does not need an accurate clock (precise, but not accurate). The second step is changing the delay routine.
#define SDA 4 // #define SCL 3 // #define SDA_PORT PORTB // #define SCL_PORT PORTB // As you can see above, we’ve redefined the ports and the pins. Again, in our example, we’re moving the I2C master over to PB3 and PB4. Now, simply redefine the pins to where you need them. Open this file in a text editor or AVR Studio and you’ll find the following: #define SDA 4 // SDA Port D, Pin 4 #define SCL 5 // SCL Port D, Pin 5 #define SDA_PORT PORTD //SDA Port D #define SCL_PORT PORTD // SCL Port D The pins are selected in the i2Cmaster.S file that comes from the original code.
For our project, we wanted to move the SCL and SDA lines them to pins PB3 and PB4. SDA and SCL are normally defined by the standard TWI libraries as PB2 and PB0. The pinout for normal use is in the picture to the right. There are two steps to adapting this to your project: change the pins and port definitions and match the delay clock speed. Below we’ll walk you through, step by step, on what we did to make this library work for the Attiny and the Atmega. We had to adapt this library for use in a project where we wanted to use the Attiny and Atmega. The library can be downloaded here and can be adapted for both the Attiny and Atmega chips. Peter Fleury has written a great I2C Master Library here.
#ATTINY85 PORT PINS ADDRESS HOW TO#
While there are many examples of how to use I2C and other 2-wire protocols on Atmel chip’s designated pins, how do you develop an I2C master on non-standard pins? it’s an invaluable way to reach sensors in microcontroller projects.
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