ST92185B datasheet(144/178 Pages) STMICROELECTRONICS

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ST92185B - SERIAL PERIPHERAL INTERFACE (SPI)

SERIAL PERIPHERAL INTERFACE (Cont’d)

Figure 88. SPI I/O Pins

7.6.4 Interrupt Structure

The SPI peripheral is associated with external in-

terrupt channel B0 (pin INT2). Multiplexing be-

tween the external pin and the SPI internal source

is controlled by the SPEN and BMS bits, as shown

in Table 1 Interrupt Configuration.

The two possible SPI interrupt sources are:

– End of transmission (after each byte).

– S-bus/I2C-bus start or stop condition.

Care should be taken when toggling the SPEN

and/or BMS bits from the “0,0” condition.

Before

changing the interrupt source from the external pin

to the internal function, the B0 interrupt channel

should be masked. EIMR.2 (External Interrupt

Mask Register, bit 2, IMBO) and EIPR.2 (External

Interrupt Pending Register bit 2, IMP0) should be

“0” before changing the source. This sequence of

events is to avoid the generating and reading of

spurious interrupts.

A delay instruction lasting at least 4 clock cycles

(e.g. 2 NOPs) should be inserted between the

SPEN toggle instruction and the Interrupt Pending

bit reset instruction.

The INT2 input Function is always mapped togeth-

er with the SCK input Function, to allow Start/Stop

bit detection when using S-bus/I2C-bus protocols.

A start condition occurs when SDI goes from “1” to

“0” and SCK is “1”. The Stop condition occurs

when SDI goes from “0” to “1” and SCK is “1”. For

both Stop and Start conditions, SPEN = “0” and

BMS = “1”.

Table 27. Interrupt Configuration

SPI

PORT

LATCH

SDI

SCK

INT2

SDO

SCK

SDO

SDI

INT2

BIT

PORT

LATCH

BIT

PORT

LATCH

BIT

SPEN

BMS

Interrupt Source

External channel INT2

S-bus/I2C bus start or stop condition

End of a byte transmission

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