Infineon S6BT112A User manual

Application Note Please read the Important Notice and Warnings at the end of this document 002-27376 Rev. *A

www.infineon.com page 1 of 19 2021-06-15

AN227376

Getting Started with CXPI Transceiver

S6BT112A

About this document

Scope and purpose

AN227376 introduces you to the Japanese Automotive Standards Organization (JASO) Clock Extension

Peripheral Interface (CXPI)-compliant S6BT112A transceiver chip, which has the unique wave-shaping function

for low Electromagnetic Interference (EMI). This application note describes an example of hardware connection

with the CXPI data link controller (MCU) and the CXPI bus line. In addition, it explains how the data link

controller shifts the operation mode and arbitrates transmission with the CXPI protocol.

Associated Part Family

S6BT112A

Related Documents

S6BT112A Datasheet

Table of contents

About this document....................................................................................................................... 1

Table of contents............................................................................................................................ 1

1CXPI communication protocol ................................................................................................. 3

2S6BT112A CXPI transceiver...................................................................................................... 4

3Hardware configuration.......................................................................................................... 6

3.1 Master node connection example ..........................................................................................................6

3.2 Slave node connection example.............................................................................................................6

4Software configuration........................................................................................................... 8

4.1 Mode transition .......................................................................................................................................8

4.1.1 Mode transition diagram ...................................................................................................................8

4.1.2 Transition from Normal mode to Sleep mode..................................................................................9

4.1.3 Transition from Sleep mode to Normal mode................................................................................10

4.1.3.1 Master node trigger.....................................................................................................................10

4.1.3.2 Slave node trigger.......................................................................................................................11

4.2 Arbitration .............................................................................................................................................13

Application Note 2 of 19 002-27376 Rev. *A

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Getting Started with CXPI Transceiver S6BT112A

CXPI communication protocol

4.3 Baud rate detection period and fail-safe decode initialization...........................................................15

4.3.1 Baud rate detection period..............................................................................................................15

4.3.2 Fail-safe decode initialization..........................................................................................................16

5Glossary...............................................................................................................................17

Revision history.............................................................................................................................18

Application Note 3 of 19 002-27376 Rev. *A

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Getting Started with CXPI Transceiver S6BT112A

CXPI communication protocol

1CXPI communication protocol

CXPI is a communication protocol that consists of three layers: application layer, data link layer, and physical

layer. It has the following features:

•Non-destructive CSMA / CR (carrier sense multiple access/collision resolution) method that ensures high

responsiveness even when many nodes are connected. Similar to Controller Area Network (CAN), the CXPI

protocol provides for event transmission and communication between each node.

•The slave node does not need an external oscillator to extract the data from the bus. It will use the master

clock because the master node sends a clock pulse with data and the slave node synchronizes with the

master clock bit by bit.

•Most general-purpose microcontrollers supports CXPI because it uses UART PHY.

CXPI has the following main features:

•Application layer

−Supports sleep and wakeup

•Data link layer

−Communication through non-destructive type CSMA/CR

−Uses 8 types of error detection including 8-bit /16-bit CRC

−Supports non-destructive mediation of frames

•Physical link layer

−Bus type for network topology

−Single line for communication

−Maximum 16 nodes

−Bus connection length: Maximum 40 m

−Synchronized every PWM bit

−Transfer rate: Maximum 20 kbps

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Getting Started with CXPI Transceiver S6BT112A

S6BT112A CXPI transceiver

2S6BT112A CXPI transceiver

The S6BT112A series is a CXPI transceiver that conforms to the JASO CXPI protocol. S6BT112A01 has a built-in

Spread Spectrum Clock Generator (SSCG), while S6BT112A02 has no SSCG. The S6BT112A series has the

following features.

•Operating power supply voltage range: 5.3 V to 18 V

•BUS breakdown voltage: ± 40 V

•ESD breakdown voltage: HBM ± 8 kV

•Support bitrate: 2.4 kbps ~ 20 kbps

The S6BT112A series employs many Cypress-proprietary EMI reduction countermeasure circuits. With these

technologies listed in Table 1, S6BT112A provides the industry’s best low-noise CXPI performance. By

deploying S6BT112A to both the master node and the slave node, significant noise reduction can be obtained.

Table 1 S6BT112A EMI reduction countermeasure circuit

Feature

Measures and effects

Applicable node

Optimal slew rate

control

Harmonics are reduced by lowering the slew rate.

Master / Slave

Optimal control of duty

cycle of the master

clock

By optimally controlling the master clock duty cycle,

harmonics in the keyless frequency band are reduced.

Master

SSCG (Spread

spectrum clock

generator)

The noise peak level is reduced by changing the periodic

frequency of the transceiver’s built-in clock slightly.

Master

Slave bus response

timing optimization

Automatically adjusts the slave to send the LOW pulse too

early or too late to reduce current noise (inductive noise). It

also reduces the noise of the keyless band.

Slave

Figure 1 shows a block diagram of the S6BT112A CXPI transceiver. Table 2 shows the pin functions.

Figure 1 S6BT112A block diagram

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Getting Started with CXPI Transceiver S6BT112A

S6BT112A CXPI transceiver

Table 2 S6BT112A pin functions

Pin name

I/O

Function

RXD

Receive UART data output pin

NSLP

Sleep control pin

‘0’: Sleep mode

‘1’: Normal mode / standby mode

CLK

For master node (SELMS = ‘0’): Baud rate clock input pin

Slave node (SELMS = ‘1’): Baud rate clock output pin

NSLP = HIGH: Decoding BUS clock output

NSLP = LOW: Bus clock output without decoding

TXD

Transmit UART data input pin

GND

–

Ground pin

BUS

I/O

Bus line input / output pin

BAT

–

Battery power input pin

SELMS

Master / slave switching pin

‘0’: Master

‘1’: Slave

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Getting Started with CXPI Transceiver S6BT112A

Hardware configuration

3Hardware configuration

3.1 Master node connection example

When using S6BT112A as a master node, pull down the master / slave switching pin (SELMS: 8 pin). The baud

rate clock, generated by the master node using the MCU timer, is the input to the clock input pin (CLK: 3 pin).

Note that, the MCU UART baud rate and timer output need not be synchronized. The TXD and RXD pins are

connected to the MCU's UART pin, and the BUS pin is pulled up to VBATTERY with a 1-kΩ resistor. The NSLP pin

controls the S6BT112A mode transition between the Sleep mode and the Normal mode after power-on with the

GPIO of the MCU.

Figure 2 shows the master node circuit connection (example using Traveo II MCU).

220 pF

+5 V or +3.3 V

S6BT112A

RXD

NSLP

CLK

TXD

SELMS

BAT

BUS

GND

BUS

GND

10 kΩ

10 µF

10 kΩ

0.1 µF

GND

CYT2B9

VDDD

GND

P20-5/

CXPI3_RX

P12-5/

GPIO

P14-6/

PWM

P20-6/

CXPI3_TX

GND R6

1N4148

1 kΩ

TVII R2

10 kΩ

Figure 2 Example of master node connection consisting of Traveo II MCU and S6BT112A

3.2 Slave node connection example

When using S6BT112A as a slave node, pull up the master / slave switching pin (SELMS: 8 pin). The clock output

pin (CLK: 3 pin) is connected to the MCU external interrupt pin, GPIO input pin, etc. It is used to detect the

wakeup pulse in the Sleep mode, or to measure the communication baud rate in the Normal mode and the

baud rate on the MCU side. Connect the TXD and RXD pins to the MCU's UART pin. The NSLP pin controls the

S6BT112A mode transition between the Sleep mode and the Normal mode after power on with the GPIO of the

MCU.

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Getting Started with CXPI Transceiver S6BT112A

Hardware configuration

Figure 3 shows circuit connection of slave nodes (this example uses PSoC 4).

220 pF

+5 V or +3.3 V

S6BT112A

RXD

NSLP

CLK

TXD

SELMS

BAT

BUS

GND

R3 +B

BUS

GND

10 kΩ

10 µF

10 kΩ

0.1 µF

GND

PSoC4100S

Plus

VDD

GND

P1.0/

uart_rx

P0.1/

in_n

P3.0/

P1.1/

uart_tx

10 kΩ

Figure 3 Connection example of slave node configured with PSoC 4 and S6BT112A

In case of adding the secondary clock master operation, the SELMS pin must be connected to the GPIO of the

MCU in addition to being pulled up. When switching to the secondary clock master operation in the power on

state, make sure that the NSLP pin is set to LOW and transition to the Sleep mode, and after confirming that

there is no communication such as Wakeup pulse on the BUS at the CLK pin, switch the SELMS pin to LOW.

Input the baud rate clock to the CLK pin.

Application Note 8 of 19 002-27376 Rev. *A

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Getting Started with CXPI Transceiver S6BT112A

Software configuration

4Software configuration

4.1 Mode transition

4.1.1 Mode transition diagram

Figure 4 shows the mode transition diagram of S6BT112A.

Figure 4 Mode transition diagram of S6BT112A

S6BT112A mainly has the following three operating modes:

•Sleep mode

•Standby mode

•Normal mode

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Getting Started with CXPI Transceiver S6BT112A

Software configuration

By controlling the NSLP pin, it is possible to transition between the three modes. To suppress the power

consumption of nodes that are constantly supplied with power, it is possible to transition to the power-saving

Sleep mode. In systems where power is supplied only when needed, you can choose not to use the

Wakeup/Sleep function.

Sleep mode is a power-saving mode in which each node stops sending and receiving data. All nodes transition

to Sleep mode after the power is turned on. Ensure that you turn on the power with NSLP = LOW. During Sleep

mode, the BUS signal is received without being decoded, and will be transmitted out from the RXD terminal at

the master node and from the CLK terminal at the slave node.

Standby mode is a transient mode during the transition from Sleep mode to Normal mode. During Standby

mode, transmission and reception output are suspended. When setting NSLP to HIGH, S6BT112A first

transitions to Standby mode. After the TMODE_CHG time, S6BT112A transitions to Normal mode automatically.

Normal mode is a mode in which communication is possible. During Normal mode, the transmission data,

which is input to the TXD terminal is encoded and output to the BUS line. The received BUS data is decoded

and output to the RXD terminal.

In addition to the operating modes, there are ThermalShutdown mode and WP_ThermalShutdown mode as

failsafe functions to prevent malfunctions at abnormally high device temperature. In Thermal Shutdown mode,

the clock or data from the MCU to the BUS will be stopped, but the decoded BUS signal can be monitored by

the output of the CLK terminal or RXD terminal. In WP_ThermalShutdown mode, the non-decoded BUS signal

can be monitored by the output of CLK terminal. When the temperature falls to the normal range, S6BT112A

transitions from WP_ThermalShutdown mode to Sleep mode.

4.1.2 Transition from Normal mode to Sleep mode

When the Sleep condition is met, the master node can transmit a Sleep frame.

The master node stops the clock output at Tclock_stop_m time after receiving the Sleep frame. When the slave node

receives the Sleep frame, it prepares for Sleep and sleeps at Tsleep_s time (see JASO D015-3 for Tclock_stop_m time

and Tsleep_s time).

S6BT112A transitions to Sleep mode by changing the NSLP pin from HIGH to LOW. Set the master node CLK pin

to HIGH in Sleep mode. Also, set the TXD pin to HIGH when not communicating according to the UART protocol.

The transition flow chart and timing chart from Normal mode to Sleep mode are shown in Figure 5 and

Figure 6 respectively.

Figure 5 Transition flow from Normal mode to Sleep mode

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Getting Started with CXPI Transceiver S6BT112A

Software configuration

Figure 6 Transition timing from Normal mode to Sleep mode

4.1.3 Transition from Sleep mode to Normal mode

4.1.3.1 Master node trigger

When the master node detects an internal factor event such as sensor detection in Sleep mode, it sets the NSLP

pin of S6BT112A to HIGH to transition back to Normal mode. In addition, the master node will transmit the

baud rate clock to the transceiver CLK pin to transmit the clock to the communication bus.

In the slave node, when S6BT112A receives the BUS clock, it outputs the non-decoded clock signal from the CLK

terminal. With that as a trigger, the MCU sets the NSLP pin of S6BT112A to HIGH within Twakeup_s time to

transition to Standby mode. Upon receiving the clock from the bus, and the slave node will transition to Normal

mode (see JASO D015-3 for Twakeup_s time) from standby mode.

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