SMS44
Acknowledge Polli ng
Current Address Read ( memory only )
WhentheSMS44isperforminganinternalWRITEopera- The SMS44 contains an internal address counter which
tion it will ignore any new START conditions. Since the maintains the address of the last word accessed, incre-
device will only return an acknowledge after it accepts the mentedbyone. Ifthelastaddressaccessed(eitheraread
START the part can be continuously queried until an orwrite)wastoaddresslocationn,thenextreadoperation
acknowledgeisissued, indicatingthattheinternalWRITE would access data from address location n+1 and incre-
cycle is complete. See the flow diagram for the proper ment the current address pointer. When the SMS44
sequence of operations for polling.
receives the slave address field with the R/W bit set to “1,”
it issues an acknowledge and transmits the 8-bit word
stored at address location n+1. The current address byte
read operation only accesses a single byte of data. The
master does not acknowledge the transfer, but does
generate a stop condition. At this point, the SMS44
discontinues data transmission.
Write Cycle
In Progress
Issue Start
Random Address Read ( Regi ster and Memory )
Issue Stop
Random address read operations allow the master to
access any memory location in a random fashion. This
operation involves a two-step process. First, the master
issuesawritecommandwhichincludesthestartcondition
andtheslaveaddressfield(withtheR/WbitsettoWRITE),
followed by the address of the word it is to read. This
proceduresetstheinternaladdresscounteroftheSMS44
to the desired address. After the word address acknowl-
edge is received by the master it immediately reissues a
start condition, followed by another slave address field
withtheR/WbitsettoREAD. TheSMS44willrespondwith
an acknowledge and then transmit the 8 data bits stored
attheaddressedlocation. Atthispointthemasterdoesnot
acknowledgethetransmissionbutdoesgeneratethestop
condition. The SMS44 discontinues data transmission
and reverts to its standby power mode.
Issue Slave
Address and
R/W = 0
No
ACK
Returned
Yes
Next
Operation
a Write?
No
Yes
Issue Stop
Issue
Address
Sequenti al READ ( Memory Only )
Sequential reads can be initiated as either a current
address READ or random access READ. The first word
is transmitted as with the other byte read modes (current
address byte READ or random address byte READ);
however, the master now responds with an ACKnowl-
edge, indicating that it requires additional data from the
SMS44. The SMS44 continues to output data for each
ACKnowledge received. The master terminates the se-
quential READ operation by not responding with an AC-
Knowledge,andissuesastopcondition. Duringasequen-
tial read operation the internal address counter is auto-
matically incremented with each ACKnowledge signal.
For read operations all address bits are incremented,
allowing the entire array to be read using a single read
command. After a count of the last memory address the
address counter will ‘roll-over’ and the memory will con-
tinue to output data.
Proceed
With
Await
Next
Write
Command
2047 Fig11 2.1
Fi gure 11.
Wri te Flow Chart
READ OPERATI ON S
Read operations are initiated with the R/W bit of the
identification field set to “1.” T here are two different read
options: 1. Current Address Byte Read, and 2. Random
Address Byte Read
SUMMIT MICROELECTRONICS, Inc.
2047 2.3 10/23/00
14
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
