Evaluates: MAX6901
MAX6901 Evaluation System/Evaluation Kit
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Quick Start
Required Equipment
Before you begin, the following equipment is needed:
•Maxim MAX6901EVKIT and MAXSMBus interface
board
•12VDC power supply (Any supply voltage between
+9V and +15V is acceptable.)
•Computer running Windows 95 or 98
•Spare parallel port
•25-pin I/O extension cable
Procedure
1) Carefully connect the boards by aligning the 20-pin
connector of the MAX6901 EV kit with the 20-pin
header of the MAXSMBus interface board. Gently
press them together. The two boards should be flush
against each other.
Do not turn on the power until all connections are
made.
2) Connect the 25-pin I/O extension cable from the
computer’s parallel port to the MAXSMBus board.
The EV kit software uses a loopback connection to
confirm that the correct port has been selected.
3) Install the EV system software on your computer by
running the INSTALL.EXE program on the floppy
disk. The program files are copied and icons are
created for them in the Windows Start menu.
4) Ensure that the jumper settings are in the default
position (Table 1).
5) Connect the 12VDC power supply to the
MAXSMBus board between POS9 and GND.
Voltage for the MAX6901 ICs comes from the
MAXSMBus board.
6) Start the program by opening its icon in the Start
menu.
7) Click on the Set from Computer’s Clock button to
write the current time of day into the MAX6901.
8) Observe the difference between the computer’s time
and the MAX6901 time. The offset is calculated by
Offset = RTC time - PC time. In general, the RTC
keeps more accurate time than the PC. To determine
long-term accuracy of the RTC, it must be set by and
checked against an accurate time source. The easi-
est way to do this using the MAX6901 EV software is
to use an Internet time service to set the PC clock and
then set the RTC from the PC clock. This Internet time
service can then be used to accurately update the PC
clock regularly for an accurate comparison of the
RTC against a known time standard. The National
Institute of Standards and Technology (NIST) offers
such an Internet time service without charge
(http://www.boulder.nist.gov/timefreq/service/its.htm).
Note: The MAX6901EVSYS may be unplugged from the
parallel port for long-term drift testing.
Detailed Description of
Hardware
The MAX6901 (U1) is a real-time clock with RAM. The
MAX1840 level translator (U2) is not required for normal
operation of the MAX6901, but allows operation at supply
voltages down to +2V, while still communicating with the
MAXSMBus board, which is using +5V logic levels. See
Figure 7 and refer to the MAX6901 data sheet.
Measuring Timekeeping Supply Current
The MAX6901 is in standby mode whenever no com-
mands are being sent. To measure the timekeeping
supply current drawn in standby mode, first ensure that
the main screen’s Cyclic Burst Read checkbox is not
checked, disable the 32kHz output by checking the
32kHz Disable checkbox, remove the shunt from JU2,
and measure the voltage across R1. A voltage drop of
10mV represents 200nA of timekeeping supply current.
For active bus operation (serial bus activity), replace
shunt JU2 to prevent excessive voltage drop across
resistor R1.
Surface-Mount Crystal
The EV kit comes with a 1.1mm cylindrical tuning fork
crystal; however, the PC board layout accommodates an
optional surface-mount crystal. Only one crystal may be
used.
Table 1. Jumper Functions
communication with the RTC.
voltage across R1.
this state.