Single-Phase Power-Measurement

10 _____________________________________________________________________________________

master device. The master device initiates all communi-

received over the serial data line (SDA) with respect to

the most significant bit and end with the least significant

ACK/NACK bit.

by the bus master, but can be at most 400kHz. The

MAXQ314 can hold the SCL line low while processing

commands to delay reception of further data. For fre-

quencies at or below 100kHz, the delay can be transpar-

ent, but at 400kHz delays can be noticeable.

controller returns to its default state, and the SDA and

SCL pins go their idle state.

The A2, A1, and A0 pins are latched following every

reset and used to construct the 7-bit slave address as

shown in Table 1. The pin states are represented by L for

logic 0, H for logic 1, and Z for high impedance.

packet-error checking. When packet-error checking is

enabled by setting the PECEN bit (DSPCFG.3) to 1, a

packet-error code (PEC) byte is appended at the end

of each transaction. The byte is calculated as CRC-8

checksum, calculated over the entire message including

the address and read/write bit. The polynomial used is

ized to zero).

Commands are read and write, the command code byte

being an address of a register to read/write. Data length

is 2 bytes for most registers, both read and write; 3 bytes

for power (P, Q, S, PAVG), VRMS, and IRMS read com-

mands. The MAXQ314 could be unable to report data

like power, IRMS, VRMS, etc., immediately if the read

command is received while the requested data is being

calculated. In such a case, the clock line is held low

until the calculation completes or a bus timeout occurs.

The firmware does not support ARA address or address

broadcast features.

Table 1. Slave Address Determination

A2

A1

A0

SLAVE ADDRESS :7

L

L

L

60h (1100 000b)

L

L

Z

61h (1100 001b)

L

L

H

62h (1100 010b)

L

Z

L

63h (1100 011b)

L

Z

Z

64h (1100 100b)

L

Z

H

65h (1100 101b)

L

H

L

66h (1100 110b)

L

H

Z

67h (1100 111b)

L

H

H

68h (1101 000b)

Z

L

L

69h (1101 001b)

Z

L

Z

6Ah (1101 010b)

Z

L

H

6Bh (1101 011b)

Z

Z

L

6Ch (1101 100b)

Z

Z

Z

6Dh (1101 101b)

Z

Z

H

6Eh (1101 110b)

Z

H

L

6Fh (1101 111b)

Z

H

Z

70h (1110 000b)

Z

H

H

71h (1110 001b)

H

L

L

72h (1110 010b)

H

L

Z

73h (1110 011b)

H

L

H

74h (1110 100b)

H

Z

L

75h (1110 101b)

H

Z

Z

76h (1110 110b)

H

Z

H

77h (1110 111b)

H

H

L

78h (1111 000b)

H

H

Z

79h (1111 001b)

H

H

H

7Ah (1111 010b)