PIC16 datasheet(216/418 Pages) MICROCHIP

216 / 418 page

PIC16(L)F1508/9

DS40001609C-page 216

 2011-2013 Microchip Technology Inc.

21.6.5

C MASTER MODE REPEATED

START CONDITION TIMING

A Repeated Start condition (Figure 21-27) occurs when

the RSEN bit of the SSPxCON2 register is pro-

grammed high and the master state machine is no lon-

ger 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 sam-

pled 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 21-27:

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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