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S42WD42SAP Datasheet(PDF) 10 Page - Summit Microelectronics, Inc. |
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S42WD42SAP Datasheet(HTML) 10 Page - Summit Microelectronics, Inc. |
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10 / 16 page  10 S4242/S42WD42/S4261/S42WD61 2025 6.0 4/17/00 FIGURE 12. CURRENT ADDRESS BYTE READ MODE FIGURE 11. ACKNOWLEDGE POLLING Acknowledge Polling When the S42xxx is performing an internal WRITE opera- tion, it will ignore any new START conditions. Since the device will only return an acknowledge after it accepts the START, the part can be continuously queried until an acknowledge is issued, indicating that the internal WRITE cycle is complete. To poll the device, give it a START condition, followed by a slave address for a WRITE operation (See Figure 9). READ OPERATIONS Read operations are initiated with the R/W bit of the identification field set to “1.” There are four different read options: 1. Current Address Byte Read 2. Random Address Byte Read 3. Current Address Sequential Read 4. Random Address Sequential Read Current Address Byte Read The S42xxx contains an internal address counter which maintains the address of the last word accessed, incremented by one. If the last address accessed (either a read or write) was to address location n, the next read operation would access data from address location n+1 and increment the current address pointer. When the S42xxx 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 S42xxx discontinues data transmission. See Figure 12 for the address acknowledge and data transfer sequence. Issue Start Internal WRITE Cycle In Progress; Begin ACK Polling Issue Slave Address and R/W = 0 ACK Returned? Next operation a WRITE? Issue Byte Address Proceed with WRITE Issue Stop Await Next Command Issue Stop No No Yes (Internal WRITE Cycle is completed) Yes 2025 ILL11.0 S T A R T S T O P Slave Address Device Type Address Read/Write 1= Read A10,A9,A8 SDA Bus Activity D 7 D 6 D 5 D 4 D 3 D 2 D 1 D 0 Master sends Read request to Slave Slave sends Data to Master Master Transmitter to Slave Receiver Slave Transmitter to Master Receiver 1 1 1 00 1 Lack of ACK (low) from Master determines last data byte to be read 1 Shading Denotes 42xxx SDA Output Active A 9 A 10 R W A C K A 8 Data Byte 2025 ILL12.1 |
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