ST6255CB3 datasheet(56/86 Pages) STMICROELECTRONICS

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ST62T55C ST62T65C/E65C

SERIAL PERIPHERAL INTERFACE SPI (Cont’d)

SPI DIV Register (DIV)

Address: E1h

—

Read/Write

Reset status: 00h

The SPIDIV register defines the transmission rate

and frame format and contains the interrupt flag.

Bits CD0-CD2, DIV3-DIV6 are read/write while

SPINT can be read and cleared only. Write access

is not allowed if SPRUN in the MOD register is set.

Bit 7 = SPINT:

Interrupt Flag. If SPIE bit=1, SPINT

is automatically set to one by the SPI at the end of

a transmission or reception and an interrupt re-

quest can be generated depending on the state of

the interrupt mask bit in the MOD control register.

This bit is write and read and must be cleared by

user software at the end of the interrupt service

routine.

Bit 6-3 = DIV6-DIV3:

Burst Mode Bit Clock Period

Selection. Define the number of shift register bits

that are transmitted or received in a frame. The

available selections are listed in Table 17. The

normal maximum setting is 8 bits, since the shift

er number of bits, in conjunction with the SPIN bit

in the MOD register, unwanted data bits may be fil-

tered from the data stream.

Bit 2-0 = CD2-CD0:

Base/Bit Clock Rate Selec-

tion. Define the division ratio between the core

clock (fINT divided by 13) and the clock supplied to

the Shift Register in Master mode.

Table 16. Base/Bit Clock Ratio Selection

Note: For example, when an 8MHz CPU clock is

used, asynchronous operation at 9600 Baud is

possible (8MHz/13/64). Other Baud rates are

available by proportionally selecting division fac-

tors depending on CPU clock frequency.

Data setup time on Sin is typically 250ns min, while

data hold time is typically 50ns min.

SPI Data/Shift Register (SPIDSR)

Address: E0h

—

Read/Write

Reset status: XXh

SPIDSR is read/write, however write access is not

allowed if the SPRUN bit of Mode Control register

is set to one.

Data is sampled into SPDSR on the SCK edge de-

termined by the CPOL and CPHA bits. The affect

of these setting is shown in the following diagrams.

The Shift Register transmits and receives the Most

Significant Bit first.

Bit 7-0 = DSR7-DSR0:

Data Bits. These are the

SPI shift register data bits.

Miscellaneous Register (MISCR)

Address: DDh

—

Write only

Reset status: xxxxxxxb

Bit 7-1 = D7-D1:

Reserved.

Bit 0 = D0:

Bit 0. This bit, when set, selects the

Sout pin as the SPI output line. When this bit is

cleared, Sout acts as a standard I/O line.

SPINT

DOV6

DIV5

DIV4

DIV3

CD2

CD1

CD0

CD2-CD0

Divide Ratio (decimal)

Divide by 1

Divide by 2

Divide by 4

Divide by 8

Divide by 16

Divide by 32

Divide by 64

Divide by 256

DIV6-DIV3

Number of bits sent

Reserved (not to be used)





 Refer to the

 description of the

 DIV6-DIV3 bits in

 the DIV Register



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