PIC16C923T-08I/SP View Datasheet(PDF) - Microchip Technology
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PIC16C923T-08I/SP Datasheet PDF : 189 Pages
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PIC16C9XX
11.2.2 ADDRESSING I2C DEVICES
There are two address formats. The simplest is the 7-bit
address format with a R/W bit (Figure 11-9). The more
complex is the 10-bit address with a R/W bit
(Figure 11-10). For 10-bit address format, two bytes
must be transmitted with the first five bits specifying this
to be a 10-bit address.
FIGURE 11-9: 7-BIT ADDRESS FORMAT
MSb
S
LSb
R/W ACK
slave address
S
R/W
ACK
Start Condition
Read/Write pulse
Acknowledge
Sent by
Slave
FIGURE 11-10: I2C 10-BIT ADDRESS
FORMAT
S 1 1 1 1 0 A9 A8 R/W ACK A7 A6 A5 A4 A3 A2 A1 A0 ACK
S - Start Condition
R/W - Read/Write Pulse
ACK - Acknowledge
sent by slave
= 0 for write
11.2.3 TRANSFER ACKNOWLEDGE
All data must be transmitted per byte, with no limit to the
number of bytes transmitted per data transfer. After
each byte, the slave-receiver generates an acknowl-
edge bit (ACK) (Figure 11-11). When a slave-receiver
doesn’t acknowledge the slave address or received
data, the master must abort the transfer. The slave
must leave SDA high so that the master can generate
the STOP condition (Figure 11-8).
FIGURE 11-11: SLAVE-RECEIVER
ACKNOWLEDGE
Data
Output by
Transmitter
Data
Output by
Receiver
SCL from
Master
not acknowledge
acknowledge
1
2
8
9
S
Start
Condition
Clock Pulse for
Acknowledgment
If the master is receiving the data (master-receiver), it
generates an acknowledge signal for each received
byte of data, except for the last byte. To signal the end
of data to the slave-transmitter, the master does not
generate an acknowledge (not acknowledge). The
slave then releases the SDA line so the master can
generate the STOP condition. The master can also
generate the STOP condition during the acknowledge
pulse for valid termination of data transfer.
If the slave needs to delay the transmission of the next
byte, holding the SCL line low will force the master into
a wait state. Data transfer continues when the slave
releases the SCL line. This allows the slave to move the
received data or fetch the data it needs to transfer
before allowing the clock to start. This wait state tech-
nique can also be implemented at the bit level,
Figure 11-12. The slave will inherently stretch the clock,
when it is a transmitter, but will not when it is a receiver.
The slave will have to clear the SSPCON<4> bit to
enable clock stretching when it is a receiver.
FIGURE 11-12: DATA TRANSFER WAIT STATE
SDA
MSB
SCL S
1
Start
Condition
acknowledgment
signal from receiver byte complete
interrupt with receiver
acknowledgment
signal from receiver
clock line held low while
interrupts are serviced
2
7
8
9
1
2
3•8 9
P
Address
R/W ACK Wait
State
Data
ACK
Stop
Condition
DS30444E - page 70
© 1997 Microchip Technology Inc.
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