Cirrus Logic CS5464 - Manual (Page 22)

CS5464
22 DS682F3
7. USING THE CS5464
7.1 Initialization
The CS5464 uses a power-on-reset circuit (POR) to
provide an internal reset until the analog voltage reach-
es 4.0 V. The RESET input pin can also be used by the
application circuit to reset the part.
After RESET is removed and the oscillator is stable, an
initialization program is executed to set the default reg-
ister values.
A Software Reset command is also provided to allow
the application to run the initialization program without
removing power or asserting RESET.
The application should avoid sending commands during
initialization. The DRDY bit in the Status register indi-
cates when the initialization program has completed.
7.2 Power-down States
The CS5464 has two power-down states, stand-by and
sleep. In the stand-by state, all circuitry except the volt-
age reference and crystal oscillator is powered off. In
sleep state, all circuitry except the instruction decoder is
powered off.
To return the device to the active state, send a Wake-
Up/Halt command to the device. When returning from
stand-by mode, registers will retain their contents prior
to entering the stand-by state. When returning from
sleep mode, a complete initialization occurs.
7.3 Tamper Detection and Correction
The CS5464 provides compensation for at least two
forms of meter tampering. A second current input is pro-
vided in the event that the primary input is impaired by
tampering. (See
Figure 14 on page 42). An internal
RMS voltage reference is also available in the event that
the voltage input has been compromised by tampering.
Power and energy are calculated for BOTH current in-
puts (both energy channels). The CS5464 can automat-
ically choose the channel with the greater magnitude.
The register E
MIN
, (also called Irms
MIN
) sets a minimum
level for automatic channel selection, and Ichan
LEVEL
sets a minimum difference that will allow a channel
change. Modes register bit Ichan selects the energy
channel, and is normally driven by the CS5464 pro-
gram. This affects the pulse registers and pulse energy
outputs. (See figure
8 ).
The application program can also choose the more ap-
propriate energy channel. Modes register bit Ihold dis-
ables automatic selection and Ichan can be driven by
the application. Shown below is the channel selector.
If the application detects that the voltage input has been
impaired it may choose to use the fixed internal RMS
voltage reference by setting the VFIX bit in the Modes
register. The value of this reference (VF
RMS
) is by de-
fault 0.707107 (full-scale RMS) but can be changed by
the application program. (See figure
9 )
AVG
AVG
Figure 8. Energy Channel Selection
Figure 9. Fixed RMS Voltage Selection