AT89S8252

8

Table 4. SPCR—SPI Control Register

SPCR Address = D5H

Reset Value = 0000 01XXB

SPIE

SPE

DORD

MSTR

CPOL

CPHA

SPR1

SPR0

Bit

76543210

Symbol

Function

SPIE

SPI Interrupt Enable. This bit, in conjunction with the ES bit in the IE register, enables SPI interrupts: SPIE = 1 and ES

= 1 enable SPI interrupts. SPIE = 0 disables SPI interrupts.

SPE

SPI Enable. SPI = 1 enables the SPI channel and connects SS, MOSI, MISO and SCK to pins P1.4, P1.5, P1.6, and

P1.7. SPI = 0 disables the SPI channel.

DORD

Data Order. DORD = 1 selects LSB first data transmission. DORD = 0 selects MSB first data transmission.

MSTR

Master/Slave Select. MSTR = 1 selects Master SPI mode. MSTR = 0 selects Slave SPI mode.

CPOL

Clock Polarity. When CPOL = 1, SCK is high when idle. When CPOL = 0, SCK of the master device is low when not

transmitting. Please refer to figure on SPI Clock Phase and Polarity Control.

CPHA

Clock Phase. The CPHA bit together with the CPOL bit controls the clock and data relationship between master and

slave. Please refer to figure on SPI Clock Phase and Polarity Control.

SPR0

SPR1

SPI Clock Rate Select. These two bits control the SCK rate of the device configured as master. SPR1 and SPR0 have

no effect on the slave. The relationship between SCK and the oscillator frequency, F

SPR1SPR0 SCK = F

00

4

01

16

10

64

11

128

Table 5. SPSR – SPI Status Register

SPSR Address = AAH

Reset Value = 00XX XXXXB

SPIF

WCOL

––––––

Bit

76543210

Symbol

Function

SPIF

SPI Interrupt Flag. When a serial transfer is complete, the SPIF bit is set and an interrupt is generated if SPIE = 1 and

ES = 1. The SPIF bit is cleared by reading the SPI status register with SPIF and WCOL bits set, and then accessing

the SPI data register.

WCOL

Write Collision Flag. The WCOL bit is set if the SPI data register is written during a data transfer. During data transfer,

the result of reading the SPDR register may be incorrect, and writing to it has no effect. The WCOL bit (and the SPIF

bit) are cleared by reading the SPI status register with SPIF and WCOL set, and then accessing the SPI data register.

Table 6. SPDR – SPI Data Register

SPDR Address = 86H

Reset Value = unchanged

SPD7

SPD6

SPD5

SPD4

SPD3

SPD2

SPD1

SPD0

Bit

7

65

432

10