MSP-EXP430FR5739 User Experience Demo
2.2.2.1
Measuring Current on the MSP-EXP430FR5739
While measuring the active power in a mode, the LEDs should be turned off and the UART transmissions
should be halted. This is done by pressing switch S2 while inside the mode. Switch S2 toggles the display
settings, turning them on or off as needed. Turning the display off allows the user to isolate and measure
the current consumption of the MSP430 device when executing instructions at a clock speed of 8 MHz
and writing to FRAM. In bench tests, the MSP430 I
DVCC
was measured at approximately 800
µ
A.
Note that, because of the nature of the FRAM cache, the number of accesses to FRAM memory can
greatly impact the active power consumption. Unoptimized code that performs a higher number of
accesses to FRAM can cause an increase in the measured current. It is advisable to review the compiler
settings when setting up a project using IDEs such as CCS or IAR to ensure the most efficient code and,
hence, the least active power.
The project that accompanies this document (see
) uses a level 1 optimization setting in both
IAR and CCS that is one step higher than the default optimization levels.
As mentioned previously, when measuring the I
CC
on the board, it is important to isolate the current
consumption by the MSP430FR5739 only. The measurement can be done when the board is powered via
USB or externally via a battery. When powering via the USB, it is recommended to disconnect the
emulation portion from the MSP430FR5739 device. This can be done by removing jumpers TXD, RXD,
Reset, and Test on J3. A multimeter can be used to measure the current into the MSP430FR5739 V
CC
by
removing the V
CC
jumper and placing the multimeter leads in series.
An alternate approach requires powering the board externally via the V
CC
and GND connection and
disconnecting the USB cable from the board. In this case, the multimeter can be placed in series to V
CC
by
removing the MSP_PWR jumper.
These recommendations hold true when measuring I
DVCC
in all four modes.
2.2.2.2
Displaying Results on the PC GUI
The GUI associated with this document provides details on the time elapsed in the mode, number of bytes
written, speed of FRAM, and the endurance of FRAM emulated over a 512 byte FRAM block.
The endurance is calculated based on the 10
14
program/erase cycles for the MSP430FR5739. Because
the GUI updates every one minute, the scale of reduction of FRAM endurance is very small. A more
obvious decline in endurance can be observed in Mode 2 when the endurance reduction when using flash
is emulated.
2.2.3
Using Mode 2
–
Emulating the Speed of Flash Writes
Mode 2 is entered by pressing S1 twice, followed by S2. In this mode, the maximum speed at which flash
can be written to (at a 100% active duty cycle) is emulated on FRAM.
Similar to Mode 1, on entry into Mode 2, LED8 through LED1 light up sequentially to display the speed of
emulated flash writes. Every time the LED1 through LED8 sequence is completed, an 800KB write to flash
is emulated. In this mode, FRAM is written to at approximately 12 kBps. The entire sequence requires
approximately 80 seconds, so the demo should be observed for more than one minute to see the LED
sequence roll over.
NOTE:
The time to run this sequence varies depending on the frequency source to the interval timer
(that is, the VLO).
The test uses the same scratchpad FRAM memory as Mode 1 and the same system setup. In this mode,
after every 2KB of memory is written, a UART packet is transmitted to the PC GUI to allow it to calculate
speed and endurance information.
When measuring the average power the methodology described in
needs to be followed.
9
SLAU343B
–
May 2011
–
Revised February 2012
MSP-EXP430FR5739 FRAM Experimenter Board
Copyright
©
2011
–
2012, Texas Instruments Incorporated
