User Manual

AT89S53
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
OSC.
, is as follows:
SPR1SPR0SCK = F
OSC.
divided by
004
0116
1064
1 1 128
Table 5. SPSR—SPI Status Register Data Memory - RAM
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
76543210