L9969X datasheet(43/70 Pages) STMICROELECTRONICS

43 / 70 page

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Invalid instruction/access: an instruction is invalid, if one of the following conditions is fulfilled: a) an

unused instruction code is detected (see Table 26), b) in case the previous transmission is not completed in

terms of internal data processing (violation of the minimum access-time).

If an invalid instruction is detected, no modifications of the registers of the H-bridge are allowed.

In case an unused instruction code has occurred, the data byte “FFhex” will be transmitted after having sent

the check byte. In order to guarantee the proper operation of the corresponding circuitry the active NSS

signal must be stable for at least 50ns. In addition any access is invalid if the number of SPI clock pulses

(falling edge) counted during active NSS differs from exactly 16 clock pulses.

A write access will be internally rejected (that is internal registers will not be affected) in case the number of

falling edges applied to the SPI input SCK during the access is not equal to 16.

3.2.7.4

SPI Instruction

The uppermost 2 bits of the instruction byte are reserved to feature extended chip addressing.

The individual chip address is an option and has to be defined in accordance to the SPI-Members sharing one

NSS line.

Only when the first two bits after the falling edge of NSS are matching, the H-bridge is allowed to transfer data on

SO.

Table 26. SPI Instruction byte

MSB

CPAD1

CPAD0

INST5

INST4

INST3

INST2

INST1

INST0

Bit

Name

Description

CPAD1 (INST7)

Chip Address: Mask-Option

Value: 0 (via pad configuration)

CPAD0 (INST6)

Chip Address: Mask-Option

Value: 0 (via pad configuration)

5…0

INST5

Read/Write:

Read: 0 Write: 1

4…0

INST4…0

SPI instruction

3.2.7.5

Check byte

Table 27. Check byte

MSB

Tristate Tristate

TRANS_F

Bit

Name

Description

Tri state ( high impedance )

Fixed to High

Fixed to Low

Fixed to High

Fixed to Low

Fixed to High

TRANS_F

Transfer-Failure: (reset value ‘0’)

TRANS_F = 0: Previous Transfer was recognized as valid;

L9969x

Functional description

DS14029 - Rev 6

page 43/70

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