SMS1242
orwrite)wastoaddresslocationn,thenextreadoperation
would access data from address location n+1 and incre-
ment the current address pointer. When the SMS1242
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 SMS1242
discontinues data transmission.
however, the master now responds with an ACKnowl-
edge, indicating that it requires additional data from the
SMS1242. The SMS1242 continues to output data for
each ACKnowledge received. The master terminates the
sequential READ operation by not responding with an
ACKnowledge, and issues a STOP condition. During a
sequential read operation, the internal address counter is
automatically incremented with each ACKnowledge sig-
nal. Forreadoperations,alladdressbitsareincremented,
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.
Random Address Read
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
procedure sets the internal address counter of the
SMS1242 to the desired address. After the word address
acknowledge is received by the master it immediately
reissues a start condition followed by another slave ad-
dress field with the R/W bit set to READ. The SMS1242
willrespondwithanacknowledgeandthentransmitthe8-
databitsstoredattheaddressedlocation. Atthispoint,the
master does not acknowledge the transmission but does
generate the stop condition. The SMS1242 discontinues
data transmission and reverts to its standby power mode.
Sequential READ
Sequential reads can be initiated as either a current
address READ or a random access READ. The first word
is transmitted as with the other byte read modes (current
address byte READ or random address byte READ);
2038 2.0 6/8/00
SUMMIT MICROELECTRONICS, Inc.
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SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
