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7 COMMUNICATIONS

7.1 I

2

C INTERFACE

(a)1-bytewrite (b)quickread
(c)1-byteread
(d)incrementalread
(S=Start,Sr=RepeatedStart,A = Acknowledge,N=No Acknowledge,andP =Stop).
FuelGaugeGenerated
Hostgenerated
bq27500
bq27501System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
The fuel gauge supports the standard I
2
C read, incremental read, one-byte write quick read, andfunctions. The 7-bit device address (ADDR) is the most significant 7 bits of the hex address and is fixed as1010101. The 8-bit device address is therefore 0xAA or 0xAB for write or read, respectively.
Figure 7-1. Supported I
2
C Formats
The quick read returns data at the address indicated by the address pointer. The address pointer, aregister internal to the I
2
C communication engine, increments whenever data is acknowledged by thebq27500 or the I
2
C master. Quick writes function in the same manner and are a convenient means ofsending multiple bytes to consecutive command locations (such as two-byte commands that require twobytes of data).
Attempt to write a read-only address (NACK after data sent by master):
Attempt to read an address above 0x7F (NACK command):
Attempt at incremental writes (NACK all extra data bytes sent):
Incremental read at the maximum allowed read address:
The I
2
C engine releases both SDA and SCL if the I
2
C bus is held low for t
(BUSERR)
. If the fuel gauge washolding the lines, releasing them frees the master to drive the lines. If an external condition is holdingeither of the lines low, the I
2
C engine enters the low-power sleep mode.
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