3
AN1176.0
June 20, 2005
Note that for long recordings of deviation, it is advisable to
use a PC program that automatically updates the PC time,
such as that available from NIST:
http://www.boulder.nist.gov/timefreq/service/its.htm
Temperature Compensation
Compensation for crystal frequency variation over
temperature is accomplished using the Temperature
Compensation Settings window. Click on the thermometer
icon in the menu bar to open this window. There are six
different ranges of temp control available from 0°C to 60°C.
Slide the control bar up or down to change the setting for a
particular range. To save settings, click the Write button.
Click on the Temperature Compensation Enabled button
start using the temp compensation. Note that when using the
data recorder is functioning, temp compensation is
automatically enabled.
DEVIATION STATISTICS
Click the Bell curve icon in the menu bar. The time and
temperature statistics are presented here for the current
chart recorder data.
DAUGHTERCARD ON/OFF CONTROL
The normally open switch icon in the menu bar controls
whether V
CC
power is applied to the daughtercard. Click on
the icon once to shut off V
CC
power and the icon will turn
from black to grey. Click again on the icon to reapply V
CC
power and the icon will turn black. Note that when V
CC
power is turned off, the RTC device will operate from backup
power selected by JP2 on the motherboard. No
communication with the device is possible in backup mode.
Event-Detection Software
The Event-Detection window (shown here) is opened by
clicking on the pushbutton switch icon in the menu bar. The
button functions are defined as follows:
FIGURE 2. EVENT-DETECTION WINDOW
ENABLE EVENT MODE
This will enable the event detection function (set EVEN bit to
“1”) and put it into a standard mode with input debouncing
enabled (ESYSx set to 01) and sampling enabled (ESMPx
set to 01). The Event Register is set to 00010101b. The
software will poll the Status Register once per second to test
the EVT bit. If the EVT bit is set to “1”, then the software will
read and display the time of the event.
DISABLE EVENT MODE
Disables the Event Mode. Resets the EVEN, EVENx, and
ESMPx bits to “0”and stops polling of the Event Register.
CLEAR EVENT
Resets the EVT bit to “0”. The Event
Input will ignore any
activity on the Event Input pin while the EVT bit is set to 1.
CLEAR EVENT LOG
This will clear the window display of all recorded times of
events. The window display will retain the list of events, even
when closed, until the Clear Event Log button is selected.
Hardware and Software Detailed
Descriptions
USB RTC Evaluation Board - General Description
The evaluation board consists of the motherboard and
daughtercard. The motherboard contains all the main
support functions for the RTC device, including:
• Microcontroller for communicating with the PC and the
RTC using serial interfaces.
• USB interface IC for translating the PC USB interface to
the microcontroller serial port interface.
• Regulator to produce 3.3V from the 5V board supply.
• Connectors for the USB interface and the daughtercard.
• A 0.22F supercapacitor and a 3V CR2032 lithium battery
for backup power.
• Jumpers for selecting the backup battery or
supercapacitor, and also for selecting the V
CC
voltage of
5V or 3.3V.
• A MOSFET switch for disconnecting the V
CC
supply to the
daughtercard for backup testing.
• EEPROM and microprocessor reset (X40411) for storing
temperature data.
The daughtercard contains the Intersil RTC device, crystal,
temperature sensor IC, decoupling capacitor, and pullup
resistor for the open drain output.
Evaluation Board - Functional Description (see
Figure 3 and schematic file RTC_USB_schem.pdf)
POWER SUPPLY
The motherboard draws its power from the USB +5V ±5%
supply. If the eval board is used to provide power for other
circuitry, care must be taken to keep the current draw on this
supply well below 500mA which is the maximum for a USB
hub-type device. There is an on-board regulator (ICL7663,
U2) which produces 3.3V. The V
CC
for the Intersil RTC chip
as well as the serial interface pullup resistors is selectable
using JP1 for either 3.3V or 5V. V
CC
power can be obtained
Application Note 1176
