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
VOH 1.44     V At RPULLUP (min)  
VOL     0.45 V At RPULLUP (min)  
ISOURCE     1.5 mA    
ISINK     1.5 mA    
RPULLUP 1.2     kΩ To +VDD1 supply The resistance value of RPULLUP 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
TRISE 13   17 ns 20% to 80% All AC measurements were made with RPULLUP  at 1.2 k and with 10 pF capacitive loading.
TFALL 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
VOH V1P8V0-0.45     V    
VOL     0.45 V    
RPULLUP   1.1   kΩ To +VDD1 supply  

 

RTC Clock AC Specifications (1.8 volt pullup)

Parameter Min Typ Max Units Conditions Note
TRISE 1 5 25 ns 10% to 90%

Capacitive loading during measurements was 47 pF.

TFALL 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
VOH +V3P3V-0.45     V At RPULLUP (max)  
VOL     0.45 V At RPULLUP (min)  
RPULLUP 1.5 2.2 4.9 kΩ To +V3P3V supply  
ISOURCE     3 mA    
ISINK     3 mA    

 

RTC Clock AC Specifications (3.3 volt pullup)

Parameter Min Typ Max Units Conditions Note
TRISE 47   60 ns 20% to 80%

Capacitive loading during measurements was 47 pF.

TFALL 17   23 ns 20% to 80%
Duty Cycle 40   60 %  
Jitter     +/- 34 ppm Cycle to cycle
Frequency   32.768   kHz  

 

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