Datasheet

30
AVR068
2591C-AVR-06/06
The STK500 system clock is f
sys
= 7.37MHz., which gives the following relation
between prescaler and compare values and the resulting frequency:
f = prescaled clock / (compare value + 1) / 2
The prescale clock is the system clock divided by some factor according to this table:
Table 5-74. Prescaler values
Prescaler Value Prescaled clock frequency
0 0
1 f
sys
2 f
sys
/ 8
3 f
sys
/ 32
4 f
sys
/ 64
5 f
sys
/ 128
6 f
sys
/ 256
7 f
sys
/ 1024
The host software can compute the prescale and match values by a using a brute
force approach, scanning through all possible prescale and match values, computing
the resulting frequency, and using the parameters that gives the best result.
5.7.9 PARAM_OSC_CMATCH
This parameter only applies to STK500, not the AVRISP.
See
PARAM_OSC_PSCALE.
5.7.10 PARAM_SCK_DURATION
When using the ISP programming interface, the ISP clock frequency must not exceed
what the target device supports. (The maximum ISP clock frequency depends on the
device system clock, internal clock division etc.)