[avr-gcc-list] TWI hardware hangup issue

[Robert Conger]

Hi,
 
I'm new to the list but here goes!
 
I wrote a TWI interface for the atmega8 uC. I have four of them on a board with 
one attached to a line-driver for rs232 output. I found that I can transmit 
only once on the TWI before there is an error somewhere in the hardware and 
software. When I took a scope to the SCL and SDA lines I found that the Master 
Transmitter was transmitting as many bytes as it pleased for the first 
transmission but would only get to the start command during the second 
tranmission. After debugging with the onboard LEDs I found that the Master 
Transmitter would issue a start command but then never continue with the 
transmission. I'm using the interrupt driven approach to using the TWI and it's 
just a few switch statements and a control structure.
 
I look around on the list and found someone with a similar problem, but, it 
wasn't remedied as far as I could tell. In that instance, several bytes were 
being transmitted as individual transmissions and it would hang-up on the 
second attempt to send. Looking further I found that the datasheet lists two 
possible error conditions on the bus that could cause the hardware to fall into 
a non-active state, but, upon testing I found that those states were not 
occuring.
 
Is there anything that needs to be done to the TWI registers between 
transmissions? I just had the control register default to having the 
TWEN,TWIE,and TWEA bits set. The execution is cyclic so the exact same settings 
are used in the first transmission as the second, yet the TWI fails. Any advice 
for such a problem?


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