PIC18F23K22-ESLASHML datasheet(241/496 Pages) MICROCHIP

241 / 496 page

 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 241

PIC18(L)F2X/4XK22

15.6.5

C MASTER MODE REPEATED

START CONDITION TIMING

A Repeated Start condition occurs when the RSEN bit

of the SSPxCON2 register is programmed high and the

master state machine is no longer active. When the

RSEN bit is set, the SCLx pin is asserted low. When the

SCLx pin is sampled low, the Baud Rate Generator is

loaded and begins counting. The SDAx pin is released

(brought high) for one Baud Rate Generator count

(TBRG). When the Baud Rate Generator times out, if

SDAx is sampled high, the SCLx pin will be deasserted

(brought high). When SCLx is sampled high, the Baud

Rate Generator is reloaded and begins counting. SDAx

and SCLx must be sampled high for one TBRG. This

action is then followed by assertion of the SDAx pin

(SDAx = 0) for one TBRG while SCLx is high. SCLx is

asserted low. Following this, the RSEN bit of the

SSPxCON2 register will be automatically cleared and

the Baud Rate Generator will not be reloaded, leaving

the SDAx pin held low. As soon as a Start condition is

detected on the SDAx and SCLx pins, the S bit of the

SSPxSTAT register will be set. The SSPxIF bit will not

be set until the Baud Rate Generator has timed out.

FIGURE 15-27:

REPEAT START CONDITION WAVEFORM

Note 1: If RSEN is programmed while any other

event is in progress, it will not take effect.

2: A bus collision during the Repeated Start

condition occurs if:

• SDAx is sampled low when SCLx

goes from low-to-high.

• SCLx goes low before SDAx is

asserted low. This may indicate that

another master is attempting to

transmit a data ‘1’.

SDAx

SCLx

Repeated Start

Write to SSPxCON2

Write to SSPxBUF occurs here

At completion of Start bit,

hardware clears RSEN bit

1st bit

S bit set by hardware

TBRG

SDAx = 1,

SCLx (no change)

SCLx = 1

occurs here

TBRG

and sets SSPxIF

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