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AD7789BRMZ-REEL 데이터시트(PDF) 11 Page - Analog Devices |
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AD7789BRMZ-REEL 데이터시트(HTML) 11 Page - Analog Devices |
11 / 20 page AD7788/AD7789 Rev. B | Page 11 of 20 ON-CHIP REGISTERS The ADC is controlled and configured via a number of on-chip registers, which are described on the following pages. In the following descriptions, set implies a Logic 1 state and cleared implies a Logic 0 state, unless otherwise stated. COMMUNICATIONS REGISTER (RS1, RS0 = 0, 0) The communications register is an 8-bit, write only register. All communications to the part must start with a write operation to the communications register. The data written to the commun- ications register determines whether the next operation is a read or write operation, and to which register this operation takes place. For read or write operations, once the subsequent read or write operation to the selected register is complete, the interface returns to where it expects a write operation to the communications register. This is the default state of the interface and, on power-up or after a reset, the ADC is in this default state waiting for a write operation to the communications register. In situations where the interface sequence is lost, a write operation of at least 32 serial clock cycles with DIN high returns the ADC to this default state by resetting the entire part. Table 7 outlines the bit designations for the communications register. CR0 through CR7 indicate the bit location, CR denoting the bits are in the communications register. CR7 denotes the first bit of the data stream. The number in brackets indicates the power-on/reset default status of that bit. CR7 CR6 CR5 CR4 CR3 CR2 CR1 CR0 WEN[0] 0[0] RS1[0] RS0[0] R/W[0] CREAD[0] CH1[0] CH0[0] Table 7. Communications Register Bit Designations Bit Location Bit Name Description CR7 WEN Write Enable Bit. A 0 must be written to this bit so that the write to the communications register actually occurs. If a 1 is the first bit written, the part does not clock on to subsequent bits in the register. It stays at this bit location until a 0 is written to this bit. Once a 0 is written to the WEN bit, the next seven bits are loaded to the communications register. CR6 0 This bit must be programmed with a Logic 0 for correct operation. CR5 to CR4 RS1 to RS0 Register Address Bits. These address bits are used to select which of the ADC registers are being selected during this serial interface communication (see Table 8). CR3 R/W A 0 in this bit location indicates that the next operation is a write to a specified register. A 1 in this position indicates that the next operation is a read from the designated register. CR2 CREAD Continuous Read of the Data Register. When this bit is set to 1 (and the data register is selected), the serial interface is configured so that the data register can be continuously read, that is, the contents of the data register are placed on the DOUT/RDY pin automatically when the SCLK pulses are applied. The communications register does not have to be written to for data reads. To enable continuous read mode, the instruction 001111XX must be written to the communications register. To exit the continuous read mode, the instruction 001110XX must be written to the communications register while the DOUT/RDY pin is low. While in continuous read mode, the ADC monitors activity on the DIN line so that it can receive the instruction to exit continuous read mode. Additionally, a reset occurs if 32 consecutive 1s are seen on DIN. Therefore, DIN should be held low in continuous read mode until an instruction is to be written to the device. CR1 to CR0 CH1 to CH0 These bits are used to select the analog input channel. The differential channel can be selected AIN(+)/AIN(− ) or an internal short AIN(−)/AIN(−) can be selected. Alternatively, the power supply can be selected, that is, the ADC can measure the voltage on the power supply, which is useful for monitoring power supply variation. The power supply voltage is divided by 5 and then applied to the modulator for conversion. The ADC uses a 1.17 V ± 5% on-chip reference as the reference source for the analog-to-digital conversion. Any change in channel resets the filter and a new conversion is started. |
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