[En-Nut-Discussion] TWI initialization - new attempt

[Tim Tait]

Peter Sodermanns wrote:

> Hi group,
>
> now my development environment is up to date (Nut/OS 4.0.2, 
> WinAVR-20060125) but I'm still stuck with the TWI initialization problem.
>
> By now I've become modest and would be glad to see a single rising 
> edge at SCL or SDA pin.
>
>
> My scenario:
> ------------------------------------------------------------
> Ethernut 2.1B2, 1k5 pull ups and oscilloscope probes connected to port 
> D0 and D1. Terminal program at COM1.
>
>
> My test program:
> ------------------------------------------------------------
> #include <stdio.h>
> #include <io.h>
> #include <sys/version.h>
> #include <sys/event.h>
> #include <sys/timer.h>
> #include <dev/debug.h>
>
> int main(void)
> {
> u_long baud0 = 19200;
>
> NutRegisterDevice(&devDebug0, 0, 0);
> freopen("uart0", "w", stdout);
> _ioctl(_fileno(stdout), UART_SETSPEED, &baud0);
> NutSleep(200);
> printf_P(PSTR("\n\n\n"));
> printf_P(PSTR("Nut/OS:       %s\n"), NutVersionString());
>
> printf_P(PSTR("\n - initial register settings\n"));
> printf_P(PSTR(" TWAR = %02X\n"), TWAR);
> printf_P(PSTR(" TWBR = %02X\n"), TWBR);
> printf_P(PSTR(" TWCR = %02X\n"), TWCR);
> printf_P(PSTR(" TWDR = %02X\n"), TWDR);
> printf_P(PSTR(" TWSR = %02X\n"), TWSR);
>
> TWAR = 0x6F;    // slave address
> TWBR = 0xFF;    // ~ 28KHz
> TWDR = 0x55;    // some data
> TWSR = 0x00;    // clear status and prescaler
> // TWCR = 0xE5;    // TWINT=1, TWEA=1, TWSTA=1, TWSTO=0, TWWC=0, 
> TWEN=1, 0, TWIE=1
> TWCR = 0xA4;    // TWINT=1, TWEA=0, TWSTA=1, TWSTO=0, TWWC=0, TWEN=1, 
> 0, TWIE=0
> // TWCR = 0x24;    // TWINT=0, TWEA=0, TWSTA=1, TWSTO=0, TWWC=0, 
> TWEN=1, 0, TWIE=0
>
> printf_P(PSTR("\n - new register settings\n"));
> printf_P(PSTR(" TWAR = %02X\n"), TWAR);
> printf_P(PSTR(" TWBR = %02X\n"), TWBR);
> printf_P(PSTR(" TWCR = %02X\n"), TWCR);
> printf_P(PSTR(" TWDR = %02X\n"), TWDR);
> printf_P(PSTR(" TWSR = %02X\n"), TWSR);
>
> for (;;);    // stop here
> }
>
>
> the resulting debug output:
> ------------------------------------------------------------
> Nut/OS:       4.0.2.1
>
>  - initial register settings
>  TWAR = FE
>  TWBR = 00
>  TWCR = 00
>  TWDR = FF
>  TWSR = F8
>
>  - new register settings
>  TWAR = 6F
>  TWBR = FF
>  TWCR = 2C
>  TWDR = FF
>  TWSR = F8
>
>
> ATmega128 documentation says on p 214:
> ------------------------------------------------------------
> TWEN must be set to enable the Two-wire Serial Interface, TWSTA must 
> be written to one to transmit a START condition and TWINT must be 
> written to one to clear the TWINT flag. The TWI will then test the 
> Two-wire Serial Bus and generate a START condition as soon as the bus 
> becomes free. After a START condition has been transmitted, the TWINT 
> flag is set by hardware, and the status code in TWSR will be $08.
>
> So TWCR = 0xA4 has to be correct.
>
>
> but in real life:
> ------------------------------------------------------------
> no START condition is transmitted,
> TWINT flag is not set,
> status code is $F8 (= no state information available)
>
> I tried that with several boards.
>
>
> Question:
> ------------------------------------------------------------
> Where is the initialization bit that has to be set, too?
>
>
>
> Thankful for any hint
>
>                     Peter

Out of curiousity, what are the levels you see on SDA and SCL?

Tim