PIC16F1516 datasheet(188/344 Pages) MICROCHIP

188 / 344 page

PIC16(L)F1516/7/8/9

DS41452B-page 188

Preliminary

 2011 Microchip Technology Inc.

21.2

SPI Mode Overview

The Serial Peripheral Interface (SPI) bus is a

synchronous serial data communication bus that

operates in Full Duplex mode. Devices communicate in

a master/slave environment where the master device

initiates the communication. A slave device is

controlled through a Chip Select known as Slave

Select.

The SPI bus specifies four signal connections:

• Serial Clock (SCK)

• Serial Data Out (SDO)

• Serial Data In (SDI)

• Slave Select (SS)

Figure 21-1 shows the block diagram of the MSSP

module when operating in SPI Mode.

The SPI bus operates with a single master device and

one or more slave devices. When multiple slave

devices are used, an independent Slave Select con-

nection is required from the master device to each

slave device.

Figure 21-4 shows a typical connection between a

master device and multiple slave devices.

The master selects only one slave at a time. Most slave

devices have tri-state outputs so their output signal

appears disconnected from the bus when they are not

selected.

Transmissions involve two shift registers, eight bits in

size, one in the master and one in the slave. With either

the master or the slave device, data is always shifted

out one bit at a time, with the Most Significant bit (MSb)

shifted out first. At the same time, a new Least

Significant bit (LSb) is shifted into the same register.

Figure 21-5 shows a typical connection between two

processors configured as master and slave devices.

Data is shifted out of both shift registers on the pro-

grammed clock edge and latched on the opposite edge

of the clock.

The master device transmits information out on its SDO

output pin which is connected to, and received by, the

slave’s SDI input pin. The slave device transmits infor-

mation out on its SDO output pin, which is connected

to, and received by, the master’s SDI input pin.

To begin communication, the master device first sends

out the clock signal. Both the master and the slave

devices should be configured for the same clock polar-

ity.

The master device starts a transmission by sending out

the MSb from its shift register. The slave device reads

this bit from that same line and saves it into the LSb

position of its shift register.

During each SPI clock cycle, a full duplex data

transmission occurs. This means that while the master

device is sending out the MSb from its shift register (on

its SDO pin) and the slave device is reading this bit and

saving it as the LSb of its shift register, that the slave

device is also sending out the MSb from its shift register

(on its SDO pin) and the master device is reading this

bit and saving it as the LSb of its shift register.

After 8 bits have been shifted out, the master and slave

have exchanged register values.

If there is more data to exchange, the shift registers are

loaded with new data and the process repeats itself.

Whether the data is meaningful or not (dummy data),

depends on the application software. This leads to

three scenarios for data transmission:

• Master sends useful data and slave sends dummy

data.

• Master sends useful data and slave sends useful

data.

• Master sends dummy data and slave sends useful

data.

Transmissions may involve any number of clock

cycles. When there is no more data to be transmitted,

the master stops sending the clock signal and it dese-

lects the slave.

Every slave device connected to the bus that has not

been selected through its slave select line must disre-

gard the clock and transmission signals and must not

transmit out any data of its own.

PIC16F1516 bảng dữ liệu(PDF) 188 Page - Microchip Technology

PIC16F1516 bảng dữ liệu(HTML) 188 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

bảng dữ liệu tải về

Link URL