71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
HARDWARE DESCRIPTION
Hardware Overview
The TERIDIAN 71M6521BE single-chip energy meter integrates all primary functional blocks required to implement a solid-
state electricity meter. Included on chip are an analog front end (AFE), an independent digital computation engine (CE), an
8051-compatible microprocessor (MPU) which executes one instruction per clock cycle (80515), a voltage reference, a
temperature sensor, LCD drivers, RAM, Flash memory, and a variety of I/O pins. Various current sensor technologies are
supported including Current Transformers (CT) and Resistive Shunts.
In a typical application, the 32-bit compute engine (CE) of the 71M6521BE sequentially processes the samples from the
voltage inputs on pins IA, VA, IB, VB1 and performs calculations to measure active energy (Wh). This measurement is then
accessed by the MPU, processed further and output using the peripheral devices available to the MPU.
Measurements can be displayed on 3.3V LCD commonly used in low temperature environments. Flexible mapping of LCD
display segments will facilitate integration of existing custom LCD. Design trade-off between the number of LCD segments vs.
DIO pins can be implemented in software to accommodate various requirements.
The on-chip digital temperature compensation mechanism includes a temperature sensor and associated controls for
correction of unwanted temperature effects on measurement. Temperature dependent external components such as crystal
oscillator, current sensors, and their corresponding signal conditioning circuits can be characterized and their correction factors
can be programmed to produce electricity meters with exceptional accuracy over the industrial temperature range.
One of the two internal UARTs is adapted to support an Infrared LED with internal drive and sense configuration, and can also
function as a standard UART. The optical output can be modulated at 38kHz. This flexibility makes it possible to implement
AMR meters with an IR interface. A block diagram of the IC is shown in Figure 1. A detailed description of various functional
blocks follows.
Analog Front End (AFE)
The AFE of the 71M6521BE is comprised of an input multiplexer, a delta-sigma A/D converter and a voltage reference.
Input Multiplexer
The input multiplexer supports up to four input signals that are applied to pins IA, VA, IB and VB1 of the device. Additionally,
using the alternate multiplexer selection, it has the ability to select temperature and the battery voltage. The multiplexer can be
operated in two modes:
•
•
During a normal multiplexer cycle, the signals from the IA, IB, VA, and VB pins are selected.
During the alternate (ALT) multiplexer cycle, the temperature signal (TEMP) and the battery monitor are selected,
along with the signal sources shown in Table 1. To prevent unnecessary drainage on the battery, the battery monitor
is enabled only with the BME bit (0x2020[6]) in the I/O RAM.
The alternate multiplexer cycles are usually performed infrequently (e. g. every second or so) by the MPU. In order to prevent
disruption of the voltage tracking PLL and voltage allpass networks, VA is not replaced in the ALT multiplexer selections.
Missing samples due to an ALT multiplexer sequence are filled in by the CE.
Regular MUX Sequence
Mux State
ALT MUX Sequence
Mux State
EQU
0
1
2
3
0
1
2
3
0
IA
VA
IB
VB
TEMP
VA
IB
VBAT
Table 1: Inputs Selected in Regular and Alternate Multiplexer Cycles
1: VB is available, but not used in typical 1-phase, 2-wire meters
V1.0
© 2005-2008 TERIDIAN Semiconductor Corporation
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