3

Control interface

This section specifies the control interface. The I²C interface uses two signals: serial data line (SDA) and serial

clock line (SCL). Each device connected to the bus uses a unique address and a simple master/slave relationship

exists.

Both SDA and SCL lines are connected to a positive supply voltage using pull-up resistors located on the host.

Lines are only actively driven low. A high condition occurs when lines are floating and the pull-up resistors pull

lines up. When no data is transmitted both lines are high.

Clock signal generation is performed by the master device. The master device initiates data transfer. The I²C bus

has a maximum speed of 1 Mbits/s and uses a default device address of 0x52.

Figure 9. Data transfer protocol

1

2

7

8

Ac/Am

Start condition

Stop condition

SDA

SCL

Acknowledge

P

S

3

4

5

6

Address or data byte

MSB

LSB

Information is packed in 8-bit packets (bytes) and is always followed by an acknowledge bit, Ac for VL53L4CD

acknowledge and Am for master acknowledge (host bus master). The internal data is produced by sampling SDA

at a rising edge of SCL. The external data must be stable during the high period of SCL. The exceptions to this

are start (S) or stop (P) conditions when SDA falls or rises respectively, while SCL is high.

A message contains a series of bytes preceded by a start condition, and followed by either a stop or repeated

start (another start condition but without a preceding stop condition), followed by another message. The first byte

contains the device address (0x52) and also specifies the data direction. If the least significant bit is low (that

is, 0x52) the message is a master-write-to-the-slave. If the LSB is set (that is, 0x53) then the message is a

master-read-from-the-slave.

Figure 10. I²C device address: 0x52

MSBit

LSBit

0

1

0

1

0

0

1

R/W

All serial interface communications with the Time-of-Flight sensor must begin with a start condition. The

VL53L4CD module acknowledges the receipt of a valid address by driving the SDA wire low. The state of

the read/write bit (LSB of the address byte) is stored and the next byte of data, sampled from SDA, can be

interpreted. During a write sequence, the second byte received provides a 16-bit index which points to one of the

internal 8-bit registers.

VL53L4CD

Control interface

DS13812 - Rev 5

page 11/37