Datasheet

304
2545F–AVR–06/05
ATmega48/88/168
Notes: 1. In ATmega48/88/168, this parameter is characterized and not 100% tested.
2. Required only for f
SCL
> 100 kHz.
3. C
b
= capacitance of one bus line in pF.
4. f
CK
= CPU clock frequency
5. This requirement applies to all ATmega48/88/168 2-wire Serial Interface operation. Other devices connected to the 2-wire
Serial Bus need only obey the general f
SCL
requirement.
6. The actual low period generated by the ATmega48/88/168 2-wire Serial Interface is (1/f
SCL
- 2/f
CK
), thus f
CK
must be greater
than 6 MHz for the low time requirement to be strictly met at f
SCL
= 100 kHz.
7. The actual low period generated by the ATmega48/88/168 2-wire Serial Interface is (1/f
SCL
- 2/f
CK
), thus the low time require-
ment will not be strictly met for f
SCL
> 308 kHz when f
CK
= 8 MHz. Still, ATmega48/88/168 devices connected to the bus may
communicate at full speed (400 kHz) with other ATmega48/88/168 devices, as well as any other device with a proper t
LOW
acceptance margin.
C
i
(1)
Capacitance for each I/O Pin – 10 pF
f
SCL
SCL Clock Frequency f
CK
(4)
> max(16f
SCL
, 250kHz)
(5)
0 400 kHz
Rp Value of Pull-up resistor
f
SCL
≤ 100 kHz
f
SCL
> 100 kHz
t
HD;STA
Hold Time (repeated) START Condition
f
SCL
≤ 100 kHz 4.0 – µs
f
SCL
> 100 kHz 0.6 – µs
t
LOW
Low Period of the SCL Clock
f
SCL
≤ 100 kHz
(6)
4.7 – µs
f
SCL
> 100 kHz
(7)
1.3 – µs
t
HIGH
High period of the SCL clock
f
SCL
≤ 100 kHz 4.0 – µs
f
SCL
> 100 kHz 0.6 – µs
t
SU;STA
Set-up time for a repeated START condition
f
SCL
≤ 100 kHz 4.7 – µs
f
SCL
> 100 kHz 0.6 – µs
t
HD;DAT
Data hold time
f
SCL
≤ 100 kHz 0 3.45 µs
f
SCL
> 100 kHz 0 0.9 µs
t
SU;DAT
Data setup time
f
SCL
≤ 100 kHz 250 – ns
f
SCL
> 100 kHz 100 – ns
t
SU;STO
Setup time for STOP condition
f
SCL
≤ 100 kHz 4.0 – µs
f
SCL
> 100 kHz 0.6 – µs
t
BUF
Bus free time between a STOP and START
condition
f
SCL
≤ 100 kHz 4.7 – µs
f
SCL
> 100 kHz 1.3 – µs
Table 27-2. 2-wire Serial Bus Requirements (Continued)
Symbol Parameter
Condition Min Max Units
V
CC
0,4V–
3mA
----------------------------
1000ns
C
b
-----------------
Ω
V
CC
0,4V–
3mA
----------------------------
300ns
C
b
--------------
Ω