Datasheet

Data Sheet ADE7953
Rev. B | Page 51 of 72
COMMUNICATING WITH THE ADE7953
All ADE7953 features can be accessed via a group of on-chip
registers. For a detailed list of all the registers, see the ADE7953
Registers section. Three different communication interfaces can
be used to access the on-chip registers.
• 4-pin SPI interface
• 2-pin bidirectional I
2
C interface
• 2-pin UART interface
All three communication options use the same group of pins
and, therefore, only one method of communication should be
used in each design.
COMMUNICATION AUTODETECTION
The ADE7953 contains a detection system that automatically
detects which of the three communication interfaces is being
used. This feature allows communication to be quickly estab-
lished with minimal initialization. Autodetection works by
monitoring the status of the four communication pins and
automatically selecting the communication interface that
matches the configuration (see Table 9).
• The CS pin (Pin 28) is used to determine whether the
communication method is SPI. The pin must be low
during the SPI communication for this interface method.
The CS pin is active low and will automatically lock onto
SPI communication as a result.
• The SCLK pin (Pin 25) is used to determine whether the
communication method is I
2
C or UART. If this pin is held
high, the communication interface is set to I
2
C; if it is held
low, the communication interface is set to UART.
Therefore, although Pin 25 (SCLK) and Pin 28 (CS) are not
required if communicating via I
2
C or UA RT, the se pins should
be configured in hardware as shown in Table 9 to ensure the
functionality of the autodetection system.
LOCKING THE COMMUNICATION INTERFACE
After the selected communication interface is established, the
interface should be locked to prevent the communication
method from inadvertently changing. The ADE7953 can be
configured to lock automatically after the first successful
communication.
The automatic lock feature is disabled by default and is enabled
by clearing the COMM_LOCK bit (Bit 15) in the CONFIG
register (Address 0x102). To successfully establish and lock the
communication interface, a write should be issued shortly after
power-up to the CONFIG register, clearing the COMM_LOCK
bit and thus locking the communication interface. When the
communication interface is locked to a specific method (that is,
SPI, I
2
C, or UART), the communication method cannot be
changed without resetting the ADE7953.
Note that if using the SPI communication interface to lock
the communication mode, the CS pin must be low for a
minimum of 1.2 µs after the last SCLK. This delay is required
only when writing to the COMM_LOCK bit (see the SPI
Interface Timing section).
Table 9. Communication Autodetection
Communication Interface Pin 28 (CS) Pin 25 (SCLK) Pin 27 (MOSI/SCL/Rx) Pin 26 (MISO/SDA/Tx)
SPI 0 Don’t care MOSI MISO
I
2
C 1 1 SCL SDA
UART 1 0 Rx Tx