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HOST

bq2022

VPU

CPU

1

Communications

Controller

2

SDQ

3

VSS

VSS

UDG-02055

Serial Communication

Initialization

ROM COMMANDS

READ ROM

0

1

1

0

0

0

1

1

CRC (1 BYTE)

Reset

and

Presence

Signals

Read ROM (33h)

Family Code and Identification

Number (7 BYTES)

MATCH ROM

bq2022

SLUS526F – OCTOBER 2002 – REVISED DECEMBER 2006

Figure 1. Typical Applications Circuit

A host reads, programs, or checks the status of the bq2022 through the hierarchical command structure of the

SDQ interface. Figure 2 shows that the host must first issue a ROM command before the EPROM memory or

status can be read or modified. The ROM command either selects a specific device when multiple devices are

on the SDQ bus, or skips the selection process in single SDQ device applications.

Hidden para to force some space before figure 2 in the PDF.

Initialization

ROM Command Sequence

Memory/Status Command Sequence

Figure 2. General Command Sequence

Initialization consists of two pulses, the RESET and the PRESENCE pulses. The host generates the RESET

pulse, while the bq2022 responds with the PRESENCE pulse. The host resets the bq2022 by driving the DATA

bus low for at least 480

µs. For more details, see the RESET section under SDQ Signaling.

The READ ROM command sequence is the fastest sequence that allows the host to read the 8-bit family code

and 48-bit identification number. It is used if only one SDQ slave device is attached to the bus. The READ ROM

sequence starts with the host generating the RESET pulse of at least 480

µs. The bq2022 responds with a

PRESENCE pulse. Next, the host continues by issuing the READ ROM command, 33h, and then reads the

ROM and CRC byte using the READ signaling (see the READ and WRITE signals section) during the data

frame.

Figure 3. READ ROM Sequence

The MATCH ROM command, 55h, is used by the host to select a specific SDQ device when the family code and

identification number is known. The host issues the MATCH ROM command followed by the family code, ROM

number, and the CRC byte. Only the device that matches the 64-bit ROM sequence is selected and available to

perform subsequent Memory/Status Function commands.

5

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