PIC16F1825T-ESS datasheet(282/448 Pages) MICROCHIP

282 / 448 page

PIC16(L)F1825/1829

DS41440C-page 282

 2010-2012 Microchip Technology Inc.

25.6.13.1

Bus Collision During a Start

Condition

During a Start condition, a bus collision occurs if:

SDAx or SCLx are sampled low at the beginning

of the Start condition (Figure 25-33).

SCLx is sampled low before SDAx is asserted

low (Figure 25-34).

During a Start condition, both the SDAx and the SCLx

pins are monitored.

If the SDAx pin is already low, or the SCLx pin is

already low, then all of the following occur:

• the Start condition is aborted,

• the BCLxIF flag is set and

• the MSSPx module is reset to its Idle state

(Figure 25-33).

The Start condition begins with the SDAx and SCLx

pins deasserted. When the SDAx pin is sampled high,

the Baud Rate Generator is loaded and counts down. If

the SCLx pin is sampled low while SDAx is high, a bus

collision occurs because it is assumed that another

master is attempting to drive a data ‘1’ during the Start

condition.

If the SDAx pin is sampled low during this count, the

BRG is reset and the SDAx line is asserted early

(Figure 25-35). If, however, a ‘1’ is sampled on the

SDAx pin, the SDAx pin is asserted low at the end of

the BRG count. The Baud Rate Generator is then

reloaded and counts down to zero; if the SCLx pin is

sampled as ‘0’ during this time, a bus collision does not

occur. At the end of the BRG count, the SCLx pin is

asserted low.

FIGURE 25-33:

BUS COLLISION DURING START CONDITION (SDAX ONLY)

Note:

The reason that bus collision is not a

factor during a Start condition is that no

two bus masters can assert a Start

condition at the exact same time.

Therefore, one master will always assert

SDAx before the other. This condition

does not cause a bus collision because

the two masters must be allowed to

arbitrate the first address following the

Start condition. If the address is the same,

arbitration must be allowed to continue

into the data portion, Repeated Start or

Stop conditions.

SDAx

SCLx

SEN

SDAx sampled low before

SDAx goes low before the SEN bit is set.

S bit and SSPxIF set because

SSPx module reset into Idle state.

SEN cleared automatically because of bus collision.

S bit and SSPxIF set because

Set SEN, enable Start

condition if SDAx = 1, SCLx = 1

SDAx = 0, SCLx = 1.

BCLxIF

SSPxIF

SDAx = 0, SCLx = 1.

SSPxIF and BCLxIF are

cleared by software

SSPxIF and BCLxIF are

cleared by software

Set BCLxIF,

Start condition. Set BCLxIF.

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