PM9904BPD
ssaammeess
Getting the SA9904 to generate pulses proportional
to the energy measured.
Figure 4 is a flow diagram showing how to generate pulses
proportional to energy measured by the SA9904A. The speed
of execution is not critical, although it will influence the
resolution of the pulses that is generated.
PM9904BPDEVALUATIONSOFTWARE
Software for the SA9904AP module is supplied on one 3.5”
1.44MB floppy disk and is designed to communicate with the
SA9904AP module via the PC’s parallel port. The supplied
software is written for DOS. Additional Windows software will
be posted to the SAMES web site for downloading when
available. The source code, written in Turbo C, is also
included.
It is recommended that the flow diagram be implemented
together with a timer interrupt used for the creep timing. The
same flow diagram is applicable for the SA9604A, but reading
of the register values should be synchronized with changes in
bit D19 of its frequency register.
File description
Thefollowingfilesareincludedonthefloppydisk:
9904mtr.c
This file contains the source for the functions that read the
SA9904 registers, store these values in integration registers,
check for any overflow and generate the corresponding
energy pulse for the PM9904BPD on-board LED’s. It makes
provisiontomeasureunbalancedenergyperphaseorsumthe
energy for each phase. The software does not make use of
timers and relies on counting the software loops to generate
reasonabledelaysfortheLEDoutputs.
Read Active Register
Subtract previous value
Check and fix register value wrapping
Add to active energy integrator
pc_spi.c
This file contains the source for all the SPI interface routines
which are used to communicate between the PM9904BPD
module and the PC’s parallel port.
pc_lcd.c
No
If integrator > threshold
This file contains the source for all the functions relating to the
SA8807 LCD driver IC, as well as other functions to switch on
theLCDdisplayicons.
Wait for next measurement cycle
Do other functions on the meter
Yes
Subtract threshold from integrator
9904mtr.exe
Thisistheexecutablefile.
Load creep timer
Generate pulse
Running thesoftware
The program is executed by running the 9904mtr.exe file with
thefollowingarguments:
9904mtr.exe110
Figure 4: Pulse flow diagram
The first parameter specifies the LPT port address to use
where1= 0x378(LPT1)and2= 0x278(LPT2).
Threshold and pulse rates
The second parameter is a loop delay. Larger values will slow
down the SPI communication speed to the PM9904BPD
module.
The active and reactive registers on the SA9904B increment at
a rate of 320 000 counts per second at rated metering
conditions for a sine wave. A single count of the active register
corresponds to an amount of energy expressed in Watt
seconds (Ws).
Energy per count is (Ws):
Epc = Vnom x Imax / 320 000
4/22
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