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ADM1020AR-REEL7 Arkusz danych(PDF) 9 Page - Analog Devices |
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ADM1020AR-REEL7 Arkusz danych(HTML) 9 Page - Analog Devices |
9 / 12 page REV. 0 ADM1020 –9– In the case of the ADM1020, write operations contain ei- ther one or two bytes, while read operations contain one byte, and perform the following functions: To write data to one of the device data registers or read data from it, the Address Pointer Register must be set so that the correct data register is addressed, then data can be written into that register or read from it. The first byte of a write operation always contains a valid address that is stored in the Address Pointer Register. If data is to be written to the device, then the write operation contains a second data byte that is written to the register selected by the address pointer register. This is illustrated in Figure 12a. The device address is sent over the bus followed by R/ W set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the Address Pointer Register. The second data byte is the data to be written to the internal data register. When reading data from a register there are two possibilities: 1. If the ADM1020's Address Pointer Register value is un- known or not the desired value, it is first necessary to set it to the correct value before data can be read from the desired data register. This is done by performing a write to the ADM1020 as before, but only the data byte containing the register read address is sent, as data is not to be written to the register. This is shown in Figure 12b. A read operation is then performed consisting of the serial bus address, R/ W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 12c. 2. If the Address Pointer Register is known to be already at the desired address, data can be read from the corresponding data register without first writing to the Address Pointer Register, so Figure 12b can be omitted. NOTES 1. Although it is possible to read a data byte from a data register without first writing to the Address Pointer Register, if the Address Pointer Register is already at the correct value, it is not possible to write data to a register without writing to the Address Pointer Register, because the first data byte of a write is always written to the Address Pointer Register. 2. Don't forget that the ADM1020 registers have different ad- dresses for read and write operations. The write address of a register must be written to the address pointer if data is to be written to that register, but it is not possible to read data from that address. The read address of a register must be written to the address pointer before data can be read from that register. R/ W A6 SCLK SDATA A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY ADM1020 START BY MASTER 19 1 ACK. BY ADM1020 9 D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY ADM1020 STOP BY MASTER 1 9 SCL (CONTINUED) SDA (CONTINUED) FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 3 DATA BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 12a. Writing a Register Address to the Address Point Register, then Writing Data to the Selected Register R/ W A6 SCLK SDATA A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY ADM1020 STOP BY MASTER START BY MASTER 19 1 ACK. BY ADM1020 9 FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 12b. Writing to the Address Pointer Register Only R/ W A6 SCLK SDATA A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 NO ACK. BY MASTER STOP BY MASTER START BY MASTER 19 1 ACK. BY ADM1020 9 FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 DATA BYTE FROM ADM1020 Figure 12c. Reading Data from a Previously Selected Register |
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