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funmix
Joined: 27 Mar 2007
Posts: 33
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| Simple I2C communication between PICs |
 Posted: Fri Mar 30, 2007 11:42 pm |
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i am implementing two way communication via the I2C bus.
The data on the input to the master Port B (DIP switch) is transferred to display on the slave's Port D(LEDs) and vice versa.
I found that the LED is not lighten up.
Can someone point out what error i did in my software?
i2c_master.c
| Code: |
#include <16F877.h>
#use delay(clock=20000000)
#fuses HS,WDT
#use rs232(baud =19200,parity=N,xmit=PIN_C6,rcv=PIN_C7,stream=,bits=8)
#use i2c(Master,sda=PIN_C4,scl=PIN_C3,RESTART_WDT,FORCE_HW)
#int_TIMER1
TIMER_isr()
{
i2c_start();//set i2c to start condition
i2c_write(0xa0);//send slave address
i2c_write(input_b());//send master data from port b bits
i2c_start();//restart to change data direction
i2c_write(0xa1);//address with direction bit changed
output_d(~i2c_read(0));//get slavedata and display
i2c_stop();//stop i2c
}
void main()
{
setup_counters(RTCC_INTERNAL,WDT_1152MS);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);//pull ups for the input pins
port_b_pullups(TRUE);
enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);
while(1)
{
RESTART_WDT();//use WDT in case I2C hangs up to faulty slave
}
}
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i2c_slave.c
| Code: |
#include <16F877.h>
#use delay(clock=20000000)
#fuses HS,NOWDT
#use rs232(baud =19200,parity=N,xmit=PIN_C6,rcv=PIN_C7,stream=,bits=8)
#use i2c(SLAVE,sda=PIN_C4,SCL=PIN_C3,address=0xa0)
enum {address,data};
int mode;
#int_SSP
SSP_isr()
{
int rec;//check for valid rec received. the interrupt occurs, but no
//valid character is received when setting up for the read
if (i2c_poll())
{
rec=i2c_read();//get data received
//rec contains address on first transmission of the interchange
if(mode ==address) mode = data;//so ignore and set for data byte
else //must be data byte
{
output_D(~rec);//do output master data on LEDs
mode=address;//go back to waiting for address
}
}
//get to 'else' only if second command byte of interchange, so load
//i2c output register for read operation
else i2c_write(input_b());//load for read
}
void main()
{
port_b_pullups(true);//pull ups on input bits
enable_interrupts(INT_SSP);//interrupt mode required
enable_interrupts(global);
mode=address;//set starting mode
while(1)//main does nothing
;
}
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assuming my hardware is not causing a problem |
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Ttelmah
Guest
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| Posted: Sat Mar 31, 2007 2:45 am |
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Look at the I2C slave example.
Seriously, your 'slave', makes the _assumption_ that it is going to remain in sync with the master, and that no transactions are missed at boot up. Not a reliable thing to do. The slave needs to be looking at the I2C control bits, to find out what the interrupt is saying. You also shouldn't use I2C_poll to distinguish the data direction. The buffer full bit (which this reflects), does not get set on a slave device, when an address byte for a read is received. This is why it is _vital_ to check the address/data flag in the I2C registers.
Best Wishes |
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funmix
Joined: 27 Mar 2007
Posts: 33
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| Posted: Sun Apr 01, 2007 6:32 pm |
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Hi all,
I found two bugs in the I2C multibyte master and slave providing in code library
1. When i press 'w', then i key in the value 'askd'. When i press read (tend to read it back), the value display is 'BC4D'. 100% correct for only numbers, not for alphabet. Can i know how to solve this?
2. Using the original thread code is no problem for 16877A. But when i replace both master and slave to 18F4520, it happens that when i press 'w' and key in the value '1234' , the value return is 'FFFF'
p/s: I have changed the special function register for 18F4520.
Appreciate if someone can help to solve this |
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funmix
Joined: 27 Mar 2007
Posts: 33
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| Posted: Mon Apr 02, 2007 10:14 am |
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I understand that the maximum data can read from is FFFF.
for the problem 2,
When i replace 18F4520 as slave, the value of I2Cread is not correct.
Whatever value/integer i key in, the output is the same = FFFF.
Why does this occur? |
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