PM9904BPD
ssaammeess
Firmware
The micro-controller’s code was created according to the
guidelines set out in the evaluation software section. It is
presented as a kick-start to experimentation with the micro-
controller module and as such shouldn’t be seen as the best
(or only) possible implementation. The code was generated
using Hi-Tech PIC C (v7.86PL4); the demo version on their
www site (www.htsoft.com) is sufficient for experimentation.
Theprogramflow ispresentedinFigure9.
method of deciding what the predefined value should be is to
measure the time between two pulses at the lowest
permissible load current, this is then expressed i.t.o basic
timer ticks.
User Interface
A simple interface has been implemented using two of the
three available keys. The Enter Key toggles display of
consumed kWh and kVARh units. The Down Key displays per
phase voltage and frequency data, each press shows the next
phase’s data.
SPI
Bit-banging SPI is used to aid portability to other micros, i.e.
three port pins under direct software control creates
SPI_CLOCK, MOSI and reads MISO. The SPI access of the
SA9904B is divided into two tasks namely, fast and slow
changing data. This is accomplished via an interrupt driven
time-slicing architecture, with a basic timer tick of 10ms.
Memory Usage
ROM:
4070 words
or 50% of the total capacity
RAM:
Rate LEDs / opto-outputs
The 10ms pulse widths on these outputs are derived from the
basic timer tick.
Bank0 86%
Bank1 26%
Bank2 83%
Bank3 ---
or 50% of the total capacity
Creep
The creep algorithm is simply: - if the time between two
successive pulses is greater than a predefined maximum, the
respective energy accumulator is cleared. The simplest
Please refer to the readme. 1st file for any updated information
not contained in this application note. The mentioned file is
part of the source code that accompanies this module.
/* Switch Power on */
START
init()
Setup Ctrler’s ports and interrupts
Displays the start-up screens on LCD
boot_scrn()
Read voltage and
frequency registers.
Read energy
registers
User Interface
isr()
interrupt service routine:
10ms ticks
ctrl fast & slow tasks
ctrl pulsing of rate LEDs
Manage interrupt on key-
press
process_a_data()
process_r_data()
END
/*Power off*/
Figure 9: Program flow
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