PM9904BPD
ssaammeess
THEMICRO-CONTROLLERBOARD
OVERVIEW
Keys
This section describes the plug-in micro-controller board and
should be read in conjunction with the evaluation software
section, where basic metering software is described. The
micro-controller’s software was developed according to this
section. The board plugs into the evaluation module as
describedearlierinthisapplicationnote.
Four keys are provided of which one is connected to the micro-
controller’s reset pin. The other three are available to
implement an HMI (Human Machine Interface) in the firmware;
they’re labelled Up/Down and Enter on the printed circuit
board.
Rateoutputs
Two LEDs are provided for active and re-active energy
respectively. These pulse outputs can be coupled to an opto-
coupler via JP3/4 providing an output for external usage. This
output-pulse selection is accomplished with a jumper on JP3/4
asfollows:
1
+
+
+
Jumperonboard’soutsideedge
Jumperonboard’scentrepins
Jumperonboard’sinsideedge
= active
= re-active
= not used
Miscellaneous
Connectors JP1 and JP2 are provided to ease debugging
during code development, all relevant signals are available. J1
in conjunction with SK2 are the two plug-in points to the
evaluation module, where SK2 is the SPI connector and J1
merely a stabilising holder. The micro-controller is
programmed via SK1 using the controller’s ICSP (in circuit
serial programming) capability, as described in the relevant
MICROCHIP datasheet. If the intention is to program the board
from MICROCHIP’s PICSTART-programmer a buffer needs to
be inserted in the VDD line to boost the programmer’s output
capability. AnexampleofsuchabufferisshowninFigure8.
Figure 7: Micro-controller board
Hardware
The schematic is presented in Figure 18. As can be seen the
majorelementsare:
+
+
+
+
+
micro-controller,
eeprom,
keys,
>5V
rateLEDs/opto-isolatedratepulseoutput
andmiscellaneousconnectors.
820K
R1
100R
R3
Micro-controller
A PIC 16F876-20/so is used to generate the rate pulses, in this
application the micro uses a 20 MHz crystal (X1). This device
has 8kB Flash ROM (program memory) and 368 Byte RAM
(data memory). Detail information on the device can be
obtained in the appropriate MICROCHIP datasheet.
2N3906
EEPROM
I / P
2N3819
A 93C46 EEPROM provides storage for non-volatile data,
such as calibration factors. This device has 1 kB space
availableorstateddifferently128x8bitwords.
O / P
1.2M
R5
820K
R2
0V
Figure 8: Typical buffer circuit
6/22
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