PIC18F44J10-ESLASHML datasheet(153/358 Pages) MICROCHIP

153 / 358 page

Preliminary

DS39682C-page 151

PIC18F45J10 FAMILY

15.3.6

SLAVE MODE

In Slave mode, the data is transmitted and received as

the external clock pulses appear on SCKx. When the

last bit is latched, the SSPxIF interrupt flag bit is set.

Before enabling the module in SPI Slave mode, the

clock line must match the proper Idle state. The clock

line can be observed by reading the SCKx pin. The Idle

state is determined by the CKP bit (SSPxCON1<4>).

While in Slave mode, the external clock is supplied by

the external clock source on the SCKx pin. This

external clock must meet the minimum high and low

times as specified in the electrical specifications.

While in Sleep mode, the slave can transmit/receive

data. When a byte is received, the device will wake-up

from Sleep.

15.3.7

SLAVE SELECT

SYNCHRONIZATION

The SSx pin allows a Synchronous Slave mode. The

SPI must be in Slave mode with SSx pin control

enabled (SSPxCON1<3:0> = 04h). When the SSx pin

is low, transmission and reception are enabled and the

SDOx pin is driven. When the SSx pin goes high, the

SDOx pin is no longer driven, even if in the middle of a

transmitted byte and becomes a floating output.

External pull-up/pull-down resistors may be desirable

depending on the application.

When the SPI module resets, the bit counter is forced

to ‘0’. This can be done by either forcing the SSx pin to

a high level or clearing the SSPEN bit.

To emulate two-wire communication, the SDOx pin can

be connected to the SDIx pin. When the SPI needs to

operate as a receiver, the SDOx pin can be configured

as an input. This disables transmissions from the

SDOx. The SDIx can always be left as an input (SDIx

function) since it cannot create a bus conflict.

FIGURE 15-4:

SLAVE SYNCHRONIZATION WAVEFORM

Note 1: When the SPI is in Slave mode with SSx pin

control enabled (SSPxCON1<3:0> = 0100),

the SPI module will reset if the SSx pin is set

to VDD.

2: If the SPI is used in Slave mode with CKE

set, then the SSx pin control must be

enabled.

SCKx

(CKP = 1

SCKx

(CKP = 0

Input

Sample

SDIx

bit 7

SDOx

bit 7

bit 6

bit 7

SSPxIF

Interrupt

(SMP = 0)

CKE = 0)

(SMP = 0)

Write to

SSPxBUF

SSPxSR to

SSPxBUF

SSx

Flag

bit 0

bit 7

bit 0

Next Q4 Cycle

after Q2

↓

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