STUSB1602 datasheet(13/55 Pages) STMICROELECTRONICS

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STUSB1602

Features description

3.2

BMC interface

Figure 3. BMC interface

3.2.1

BMC interface behavior

When a connection is established on the STUSB1602 (any attached state), the CC line

used for connection is also internally connected to BMC block which allows communication

on this line.

The CC line is primary managed by CC control logic. BMC communication on the CC line

must not interact with this control logic, as driving times of the line are short and are related

to denounce times of the CC logic.

The BMC block handles BMC encoding and decoding. It also handles CC line activity

detection, discharging the external MCU of such operations.

The default state of the BMC block is to listen to the line (RX mode). TX mode is enabled

only by assertion of the TX_EN signal via the external MCU.

3.2.2

TX mode

When the TX_EN signal is asserted via the MCU, the BMC block goes to the TX state:

•

The NSS signal is driven low, indicating to the SPI/MSP slave interface of the MCU that

data are being transmitted on the CC line. The MCU provides the data.

•

The STUSB1602 drives the NSS signal low, indicating to the SPI/MSP slave interface

of the MCU that data are requested on the MISO line.

•

The STUSB1602 clocks the SCLK signal

•

The MCU presents data to be transmitted on the MISO line and data are sampled on

the rising edge of SCLK (data must be stable on this edge).

•

Sampled data (from the MISO line) are encoded by the BMC, and the resulting values

drive the CC line according to USB PD standard.

When all data are transmitted, the MCU drives the TX_EN pin low, which signals the end of

transmission. The STUSB1602 ends transmission with a corresponding trailing edge

termination. It then goes back into to default state and releases the CC line from the BMC

driver to the pull-up/pull-down CC line interfaces.

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