SMD1102 / 1103 / 1113
Start and Stop Conditions
Acknowledge
BothDataandClocklinesremainhighwhenthebusisnot Data is always transferred in 8-Bit bytes. Acknowledge
busy. Datatransferbetweendevicesmaybeinitiatedwith (ACK) is used to indicate a successful data transfer. The
aStartconditiononlywhenSCLandSDAarehigh. Ahigh- Transmitting device will release the bus after transmitting
to-lowtransitionoftheDatalinewhiletheClocklineishigh eight bits. During the ninth clock cycle the Receiver will
is defined as a Start condition. A low-to-high transition of pull the SDA line low to Acknowledge that it received the
theDatalinewhiletheClocklineishighisdefinedasaStop eight bits of data (See Figure 13). The termination of a
condition. See Figure 12.
Master Read sequence is indicated by a non-Acknowl-
edge (NACK), where the Master will leave the Data line
high.
START
Condition
STOP
Condition
SCL
In the case of a Read from a Summit part, when the last
byte has been transferred to the Master, the Master will
leave the Data line high for a NACK. This will cause the
Summitparttostopsendingdata,andtheMasterwillissue
a Stop on the clock pulse following the NACK.
SDA In
2033 Fig10
InthecaseofaWritetoaSummitparttheMasterwillsend
aStopontheclockpulseafterthelastAcknowledge. This
will indicate to the Summit part that it should begin its
internal nonvolatile write cycle.
Figure 12. Start and Stop Conditions
3
9
1
2
8
SCL
Read and Write
SDA
ThefirstbytefromaMasterisalwaysmadeupoftheeight
bits illustrated in Table 1.
Trans
SDA
Rec
ACK
InthereadmodetheSMD1102/1103/1113transmitseight
bits of data, then releases the SDA line, and monitors the
line for an Acknowledge signal. If an Acknowledge is
detected, and no STOP condition is generated by the
Master, the device will continue to transmit data. If an
Acknowledge is not detected (NACK), the device will
terminate further data transmission.
2033 Fig11
Figure 13. Acknowledge Timing
Protocol
The protocol defines any device that sends data onto the
busasaTransmitter,andanydevicethatreceivesdataas
a Receiver. The device controlling data transmission is
called the Master, and the controlled device is called the
Slave. In all cases the Summit Microelectronic devices
are slave devices, since they never initiate any data
transfers.
InthewritemodetheSMD1102/1103/1113receiveseight
bitsofdata, thengeneratesanAcknowledgesignal. Itwill
continue to generate ACKs until a STOP condition is
generated by the Master.
SUMMIT MICROELECTRONICS, Inc.
2033 8.1 10/04/01
11
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
