PIC18F44J10-ESLASHML datasheet(178/358 Pages) MICROCHIP

178 / 358 page

PIC18F45J10 FAMILY

DS39682C-page 176

Preliminary

15.4.10

I2C MASTER MODE

TRANSMISSION

Transmission of a data byte, a 7-bit address or the

other half of a 10-bit address is accomplished by simply

writing a value to the SSPxBUF register. This action will

set the Buffer Full flag bit, BF and allow the Baud Rate

Generator to begin counting and start the next trans-

mission. Each bit of address/data will be shifted out

onto the SDAx pin after the falling edge of SCLx is

asserted

(see

data

hold

time

specification

parameter 106). SCLx is held low for one Baud Rate

Generator rollover count (TBRG). Data should be valid

before SCLx is released high (see data setup time

specification parameter 107). When the SCLx pin is

released high, it is held that way for TBRG. The data on

the SDAx pin must remain stable for that duration and

some hold time after the next falling edge of SCLx.

After the eighth bit is shifted out (the falling edge of the

eighth clock), the BF flag is cleared and the master

releases SDAx. This allows the slave device being

addressed to respond with an ACK bit during the ninth

bit time if an address match occurred, or if data was

received properly. The status of ACK is written into the

ACKDT bit on the falling edge of the ninth clock. If the

master receives an Acknowledge, the Acknowledge

Status bit, ACKSTAT, is cleared; if not, the bit is set.

After the ninth clock, the SSPxIF bit is set and the

master clock (Baud Rate Generator) is suspended until

the next data byte is loaded into the SSPxBUF, leaving

SCLx low and SDAx unchanged (Figure 15-21).

After the write to the SSPxBUF, each bit of the address

will be shifted out on the falling edge of SCLx until all

seven address bits and the R/W bit are completed. On

the falling edge of the eighth clock, the master will

deassert the SDAx pin, allowing the slave to respond

with an Acknowledge. On the falling edge of the ninth

clock, the master will sample the SDAx pin to see if the

address was recognized by a slave. The status of the

ACK bit is loaded into the ACKSTAT status bit

(SSPxCON2<6>). Following the falling edge of the

ninth clock transmission of the address, the SSPxIF is

set, the BF flag is cleared and the Baud Rate Generator

is turned off until another write to the SSPxBUF takes

place, holding SCLx low and allowing SDAx to float.

15.4.10.1

BF Status Flag

In Transmit mode, the BF bit (SSPxSTAT<0>) is set

when the CPU writes to SSPxBUF and is cleared when

all 8 bits are shifted out.

15.4.10.2

WCOL Status Flag

If the user writes to the SSPxBUF when a transmit is

already in progress (i.e., SSPxSR is still shifting out a

data byte), the WCOL is set and the contents of the

buffer are unchanged (the write doesn’t occur) after

2TCY after the SSPxBUF write. If SSPxBUF is rewritten

within 2 TCY, the WCOL bit is set and SSPxBUF is

updated. This may result in a corrupted transfer.

The user should verify that the WCOL is clear after

each write to SSPxBUF to ensure the transfer is

correct. In all cases, WCOL must be cleared in

software.

15.4.10.3

ACKSTAT Status Flag

In Transmit mode, the ACKSTAT bit (SSPxCON2<6>)

is cleared when the slave has sent an Acknowledge

(ACK = 0) and is set when the slave does not Acknowl-

edge (ACK = 1). A slave sends an Acknowledge when

it has recognized its address (including a general call),

or when the slave has properly received its data.

15.4.11

I2C MASTER MODE RECEPTION

Master mode reception is enabled by programming the

Receive Enable bit, RCEN (SSPxCON2<3>).

The Baud Rate Generator begins counting and on each

rollover,

the

state

the

SCLx

changes

(high-to-low/low-to-high) and data is shifted into the

SSPxSR. After the falling edge of the eighth clock, the

receive enable flag is automatically cleared, the con-

tents of the SSPxSR are loaded into the SSPxBUF, the

BF flag bit is set, the SSPxIF flag bit is set and the Baud

Rate Generator is suspended from counting, holding

SCLx low. The MSSP is now in Idle state awaiting the

next command. When the buffer is read by the CPU,

the BF flag bit is automatically cleared. The user can

then send an Acknowledge bit at the end of reception

by setting the Acknowledge Sequence Enable bit,

ACKEN (SSPxCON2<4>).

15.4.11.1

BF Status Flag

In receive operation, the BF bit is set when an address

or data byte is loaded into SSPxBUF from SSPxSR. It

is cleared when the SSPxBUF register is read.

15.4.11.2

SSPOV Status Flag

In receive operation, the SSPOV bit is set when 8 bits

are received into the SSPxSR and the BF flag bit is

already set from a previous reception.

15.4.11.3

WCOL Status Flag

If the user writes the SSPxBUF when a receive is

already in progress (i.e., SSPxSR is still shifting in a

data byte), the WCOL bit is set and the contents of the

buffer are unchanged (the write doesn’t occur).

Note:

The MSSP module must be in an Idle state

before the RCEN bit is set or the RCEN bit

will be disregarded.

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