SMS1242S-A データシートの表示（PDF） - Summit Microelectronics

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SMS1242S-A

2.5V, 3V, 3.3V & 5V Dual Voltage, Dual Reset Microprocessor Supervisory Circuits

Summit Microelectronics 

SMS1242

or write) was to address location n, the next read operation

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.

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

issues a write command which includes the start condition

and the slave address field (with the R/W bit set to WRITE),

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

will respond with an acknowledge and then transmit the 8-

data bits stored at the addressed location. At this point, 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.

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. 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.

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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