Datasheet

AVR068
31
2591C-AVR-06/06
The STK500 and AVRISP supports ISP frequencies from 4 kHz up to 1.8 MHz. The
value for PARAM_SCK_DURATION can be found using the following algorithm:
#define T_STK500 135.63e-9
#define T_AVRISP 271.27e-9
#define B 12.0
unsigned char CalcSckDur(int freq)
{
if (STK500)
{
if (freq >= 1843200)
sck_dur = 0;
else if (freq >= 460800)
sck_dur = 1;
else if (freq >= 115200)
sck_dur = 2;
else if (freq >= 57600)
sck_dur = 3;
else
sck_dur = ceil(1/(2 * B * freq * T_STK500) - 10/B);
}
else // if (AVRISP)
{
if (freq >= 921600)
sck_dur = 0;
else if (freq >= 230400)
sck_dur = 1;
else if (freq >= 57600)
sck_dur = 2;
else if (freq >= 28800)
sck_dur = 3;
else
sck_dur = ceil(1/(2 * B * freq * T_AVRISP) - 10/B);
}
return __min(254, sck_dur); // 255 is an illegal value
}