
39
4109LS–8051–02/08
AT8xC51SND1C
7.4.6
External Clock Drive and Logic Level References
7.4.6.1
Definition of symbols
Table 43. External Clock Timing Symbol Definitions
7.4.6.2
Timings
External Clock AC Timings
VDD = 2.7 to 3.3 V, TA = -40 to +85°C
7.4.6.3
Waveforms
Figure 7-25. External Clock Waveform
Figure 7-26. AC Testing Input/Output Waveforms
Note:
1. During AC testing, all inputs are driven at V
DD -0.5 V for a logic 1 and 0.45 V for a logic 0.
2. Timing measurements are made on all outputs at V
IH min for a logic 1 and VIL max for a logic 0.
Figure 7-27. Float Waveforms
Signals
Conditions
C
Clock
H
High
L
Low
X
No Longer Valid
Symbol
Parameter
Min
Max
Unit
T
CLCL
Clock Period
50
ns
T
CHCX
High Time
10
ns
T
CLCX
Low Time
10
ns
T
CLCH
Rise Time
3
ns
T
CHCL
Fall Time
3
ns
T
CR
Cyclic Ratio in X2 mode
40
60
%
0.45 V
T
CLCL
VDD - 0.5
V
IH1
V
IL
T
CHCX
T
CLCH
T
CHCL
T
CLCX
0.45 V
VDD - 0.5
0.7 V
DD
0.3 VDD
V
IH min
VIL max
INPUTS
OUTPUTS
V
LOAD
V
OH - 0.1 V
V
OL + 0.1 V
V
LOAD + 0.1 V
V
LOAD - 0.1 V
Timing Reference Points