• 07/14/2017
  • Public Content
Contents

Clocks

The expansion board provides two clock signals on the breakout connectors, a 19.2 MHz clock and a 32.768 kHz real time clock (RTC). The following two sections provide the AC and DC specifications for both of these clock signals.
19.2 MHz System Clock
The 19.2 MHz system clock is sourced from the Intel Joule module and is routed through a LSF0108 level shifter before routing to the break out connector. Due to the high frequency of this clock, it is recommended to not level shift this signal to 3.3 V, but instead place a weak pullup to the +V1P8V supply. The system clock is on J12 on pin 5.
19.2 MHz Clock DC Specifications
Parameter
Min
Typ
Max
Units
Conditions
Note
V
OH
1.44
 
 
V
At R
PULLUP
(min)
 
V
OL
 
 
0.45
V
At R
PULLUP
(min)
 
I
SOURCE
 
 
1.5
mA
 
 
I
SINK
 
 
1.5
mA
 
 
R
PULLUP
1.2
 
 
kΩ
To +VDD1 supply
The resistance value of R
PULLUP
must be equal to or greater than the minimum resistance value provided.
 
19.2 MHz Clock AC Specifications
Parameter
Min
Typ
Max
Units
Conditions
Note
T
RISE
13
 
17
ns
20% to 80%
All AC measurements were made with R
PULLUP
 at 1.2 k and with 10 pF capacitive loading.
T
FALL
13
 
17
ns
20% to 80%
Frequency
 
19.2
 
MHz
 
Duty Cycle
45
 
55
%
 
 
32.768 kHz Real Time Clock
The 32.768 kHz real time clock (RTC) is sourced from the Intel Joule module and is routed through a LSF0108 level shifter before routing to the break out connector. The real time clock is at J13 on pin 39. A pullup resistor is required from pin 39 to the 3.3 V source. The following tables provide the DC and AC specifications for the 32.768 kHz RTC signal.
RTC Clock DC Specifications (1.8 volt pullup)
Parameter
Min
Typ
Max
Units
Conditions
Note
V
OH
V1P8V0-0.45
 
 
V
 
 
V
OL
 
 
0.45
V
 
 
R
PULLUP
 
1.1
 
kΩ
To +VDD1 supply
 
 
RTC Clock AC Specifications (1.8 volt pullup)
Parameter
Min
Typ
Max
Units
Conditions
Note
T
RISE
1
5
25
ns
10% to 90%
Capacitive loading during measurements was 47 pF.
T
FALL
1
5
25
ns
10% to 90%
Duty Cycle
40
 
60
%
 
Jitter
 
 
+/- 34
ppm
Cycle to cycle
Frequency
 
32.768
 
kHz
 
 
RTC Clock DC Specifications (3.3 volt pullup)
Parameter
Min
Typ
Max
Units
Conditions
Note
V
OH
+V3P3V-0.45
 
 
V
At R
PULLUP
(max)
 
V
OL
 
 
0.45
V
At R
PULLUP
(min)
 
R
PULLUP
1.5
2.2
4.9
kΩ
To +V3P3V supply
 
I
SOURCE
 
 
3
mA
 
 
I
SINK
 
 
3
mA
 
 
 
RTC Clock AC Specifications (3.3 volt pullup)
Parameter
Min
Typ
Max
Units
Conditions
Note
T
RISE
47
 
60
ns
20% to 80%
Capacitive loading during measurements was 47 pF.
T
FALL
17
 
23
ns
20% to 80%
Duty Cycle
40
 
60
%
 
Jitter
 
 
+/- 34
ppm
Cycle to cycle
Frequency
 
32.768
 
kHz
 
 

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Notice revision #20110804