ST92F120 datasheet(215/324 Pages) STMICROELECTRONICS

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SERIAL PERIPHERAL INTERFACE (SPI)

SERIAL PERIPHERAL INTERFACE (Cont’d)

STATUS REGISTER (SPSR)

R242 - Read Only

Reset Value: 0000 0000 (00h)

Bit 7 = SPIF

Serial Peripheral data transfer flag.

This bit is set by hardware when a transfer has

been completed. An interrupt is generated if

SPIE=1 in the SPCR register. It is cleared by a soft-

ware sequence (an access to the SPSR register

followed by a read or write to the SPDR register).

0: Data transfer is in progress or has been ap-

proved by a clearing sequence.

1: Data transfer between the device and an exter-

nal device has been completed.

Note: While the SPIF bit is set, all writes to the

SPDR register are inhibited.

Bit 6 = WCOL

Write Collision status.

This bit is set by hardware when a write to the

SPDR register is done during a transmit se-

quence. It is cleared by a software sequence (see

Figure 5).

0: No write collision occurred

1: A write collision has been detected

Bit 5 = Unused.

Bit 4 = MODF

Mode Fault flag.

This bit is set by hardware when the SS pin is

pulled low in master mode (see Section 0.1.4.5

Master Mode Fault). An SPI interrupt can be gen-

erated if SPIE=1 in the SPCR register. This bit is

cleared by a software sequence (An access to the

SPSR register while MODF=1 followed by a write

to the SPCR register).

0: No master mode fault detected

1: A fault in master mode has been detected

Bits 3:0 = Unused.

PRESCALER REGISTER (SPPR)

R243 - Read/Write

Reset Value: 0000 0000 (00h)

Bits 7:5 = Reserved, forced by hardware to 0.

Bit 4 = DIV2

Divider enable.

This bit is set and cleared by software.

0: Divider by 2 enabled.

1: Divider by 2 disabled.

Bit 3 = Reserved. forced by hardware to 0.

Bits 2:0 = PRS[2:0]

Prescaler Value.

These bits are set and cleared by software. The

baud rate generator is driven by

INTCLK/(n1*n2*n3) where n1= PRS[2:0]+1, n2 is

the value defined by the SPR[1:0] bits (refer to Ta-

ble 1 and Table 2), n3 = 1 if DIV2=1 and n3= 2 if

DIV2=0. Refer to Figure 2.

These bits have no effect in slave mode.

Table 43. Prescaler Baud Rate

SPIF

WCOL

MODF

----

DIV2

PRS2

PRS1

PRS0

Prescaler

Division Factor

PRS2

PRS1

PRS0

1 (no division)

...

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