bq2019

ADVANCED BATTERY MONITOR IC

SLUS465E – DECEMBER 1999 – REVISED FEBRUARY 2003

13

POST OFFICE BOX 655303

APPLICATION INFORMATION

communicating with the bq2019

The bq2019 includes a single-wire HDQ serial data interface. Host processors, configured for either polled or

interrupt processing, use the interface to access various bq2019 registers. The HDQ pin requires an external

pullup or pulldown resistor. The interface uses a command-based protocol, where the host processor sends a

command byte to the bq2019. The command directs the bq2019 either to store the next eight bits of data

received to a register specified by the command byte or to output the eight bits of data from a register specified

Command and data bytes consist of a stream of eight bits with a maximum transmission rate of 5 Kbits/s. The

least-significant bit of a command or data byte is transmitted first. Data input from the bq2019 may be sampled

using the pulse-width capture timers available on some microcontrollers. A UART can also communicate with

to respond or if this is the first access command), then a BREAK should be sent by the host. The host may then

resend the command. The bq2019 detects a BREAK when the HDQ pin is driven to a logic-low state for a time

ready for a command from the host processor.

The return-to-one data-bit frame consists of three distinct sections. The first section starts the transmission by

data bit. The final section stops the transmission by returning the HDQ pin to a logic-high state by at least a

timing specification and illustration sections give the timings for data and break communication. Communication

with the bq2019 always occurs with the least-significant bit being transmitted first. Figure 3 shows an example

of a communication sequence to read the bq2019 OFR register.

11

0

0

11

1

0

1

0

1

0

0

1

1

0

LSB

0

1

2

34

56

MSB

7

CMDR = 73h

Data (OFR) = 65h

LSB

0

1

2

3456

MSB

7

Break

73h = 0 1 1 1 0 0 1 1

LSB

MSB

65h = 0 1 1 0 0 1 0 1

LSB

MSB

Written By Host to bq2019

Received By Host From bq2019

t(RSPS)

Figure 3. Communication Sequence