DSPIC30F4012 datasheet(109/238 Pages) MICROCHIP

109 / 238 page

DS70135G-page 109

dsPIC30F4011/4012

16.0

SPI™ MODULE

The Serial Peripheral Interface (SPI™) module is a

synchronous serial interface. It is useful for communi-

cating

with

other

peripheral

devices,

such

EEPROMs, shift registers, display drivers and A/D

converters, or other microcontrollers. It is compatible

with Motorola’s SPI and SIOP interfaces.

16.1

Operating Function Description

The SPI module consists of a 16-bit shift register,

SPI1SR, used for shifting data in and out, and a buffer

configures the module. Additionally, a status register,

SPI1STAT, indicates various status conditions.

The serial interface consists of 4 pins: SDI1 (Serial Data

Input), SDO1 (Serial Data Output), SCK1 (Shift Clock

Input or Output), and SS1 (active-low Slave Select).

In Master mode operation, SCK1 is a clock output, but

in Slave mode, it is a clock input.

A series of eight (8) or sixteen (16) clock pulses shift

out bits from the SPI1SR to SDO1 pin, and simultane-

ously, shifts in data from SDI1 pin. An interrupt is gen-

erated when the transfer is complete and the

corresponding interrupt flag bit (SPI1IF) is set. This

interrupt can be disabled through an interrupt enable

bit (SPI1IE).

The receive operation is double-buffered. When a

complete byte is received, it is transferred from

SPI1SR to SPI1BUF.

If the receive buffer is full when new data is being

transferred from SPI1SR to SPI1BUF, the module will

set the SPIROV bit, indicating an overflow condition.

The transfer of the data from SPI1SR to SPI1BUF will

not be completed and the new data will be lost. The

module will not respond to SCL transitions while

SPIROV is ‘1’, effectively disabling the module until

SPI1BUF is read by user software.

Transmit writes are also double-buffered. The user

writes to SPI1BUF. When the master or slave transfer

is completed, the contents of the shift register

(SPI1SR) is moved to the receive buffer. If any trans-

mit data has been written to the buffer register, the

contents of the transmit buffer are moved to SPI1SR.

The received data is thus placed in SPI1BUF and the

transmit data in SPI1SR is ready for the next transfer.

In Master mode, the clock is generated by prescaling

the system clock. Data is transmitted as soon as a

value is written to SPI1BUF. The interrupt is generated

at the middle of the transfer of the last bit.

In Slave mode, data is transmitted and received as

external clock pulses appear on SCK1. Again, the

interrupt is generated when the last bit is latched. If

SS1 control is enabled, then transmission and recep-

tion are enabled only when SS1 = low. The SDO1

output will be disabled in SS1 mode with SS1 high.

The clock provided to the module is (FOSC/4). This

clock is then prescaled by the primary (PPRE<1:0>)

and secondary (SPRE<2:0>) prescale factors. The

CKE bit determines whether transmit occurs on transi-

tion from active clock state to Idle clock state, or vice

versa. The CKP bit selects the Idle state (high or low)

for the clock.

16.1.1

WORD AND BYTE

COMMUNICATION

A control bit, MODE16 (SPI1CON<10>), allows the

module to communicate in either 16-bit or 8-bit mode.

16-bit operation is identical to 8-bit operation, except

that the number of bits transmitted is 16 instead of 8.

The user software must disable the module prior to

changing the MODE16 bit. The SPI module is reset

when the MODE16 bit is changed by the user.

A basic difference between 8-bit and 16-bit operation is

that the data is transmitted out of bit 7 of the SPI1SR

for 8-bit operation, and data is transmitted out of bit 15

of the SPI1SR for 16-bit operation. In both modes, data

is shifted into bit 0 of the SPI1SR.

16.1.2

SDO1 DISABLE

A control bit, DISSDO, is provided to the SPI1CON

will allow the SPI module to be connected in an input

only configuration. SDO1 can also be used for general

purpose I/O.

Note:

This data sheet summarizes features of

this group of dsPIC30F devices and is not

intended to be a complete reference

source. For more information on the CPU,

peripherals,

descriptions

and

general device functionality, refer to the

dsPIC30F

Family

Reference

Manual

(DS70046). For more information on the

device instruction set and programming,

refer to the “16-bit MCU and DSC

Reference Manual” (DS70157).

Note:

Both the transmit buffer (SPI1TXB) and

the receive buffer (SPI1RXB) are mapped

to the same register address, SPI1BUF.

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