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AS8530

Datasheet - Application In form atio n

8.7 Serial Port Interface

The interface is essentially used to trigger the window watchdog, to access test mode and read out diagnostic information for the AS8530. The

description of this interface and the protocol is explained below. Information on block status and errors can be displayed by diagnosis registers.

8.7.1 Device Configuration using 2-Wire Serial Port

The AS8530 device configuration register is programmed via a 2-wire Serial Programming Interface. EN/SCL is used as Serial Clock and TX/

SDA_IO is used as Serial Data. EN is used as clock input to access serial port registers in serial port mode. Also EN is used to control transition

from normal mode to standby/sleep mode. The TX input of the device will be multiplexed as following:

LIN TX for transmitting data from microcontroller on LIN bus

SDA_IO for Serial data input/output, this will be used for serially accessing data from configuration and status register

number of bytes. Command is coded RD/WR on the first bits, length of the transfer is indicated by LEN1, LEN2 bits while address is given on

LSB 5 bits.

After the command code, length of the transfer is send in next two bits, the address of register to be written has to be provided from the MSB to

the LSB. Then one, two, four, or eight data bytes can be transferred from the MSB to the LSB. For each data byte following the first one, used

address is the incremented value of the previously written address. Each bit of the frame has to be driven by the 2-Wire SP master on the SP

clock (EN pin) positive edge and the 2-Wire SP slave (device) samples this bit on the next SP clock (EN pin) negative edge. In the following

figures two examples of write command (without and with address self-increment).

Figure 14. Protocol for Serial Data Write with Length = 1

Table 6. Command Bits

Command Bits

Register Address or Transmission Configuration

RD/WR

LEN1

LEN2

A4

A3

A2

A1

A0

RD/WR

Command

<A4:A0>

Description

0

WRITE

ADDRESS

Writes data byte on the given starting address.

1

READ

ADDRESS

Read data byte from the given starting address.

Table 7. Transfer Length

LEN1

LEN2

Length

Description

001

Transfer consists of single Data phase. After completion of single Data phase device comes out of Serial

port interface.

012

Transfer consist of two Data phase.

104

Transfer consist of four Data phase.

118

Transfer consist of eight Data phase.

EN

TX

0

LEN1 LEN0

A4

A0

A1

A2

A3

D0

D1

D2

D3

D4

D5

D7

D6

Transfer edge

Sampling edge

Data D7 – D0 is moved

to Address A4..A0 here

LEN1 = 0 LEN0 = 0

Command & Address Phase

Data Phase

Length of Transaction = 1