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AD7790BRM датащи(PDF) 10 Page - Analog Devices |
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AD7790BRM датащи(HTML) 10 Page - Analog Devices |
10 / 20 page AD7790 Data Sheet Rev. A | Page 10 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 communications register determines whether the next operation is a read or write oper- ation, 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 communica- tions 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 5 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 5. 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 will not clock on to subsequent bits in the register. It will stay 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 will be loaded to the communications register. CR6 0 This bit must be programmed to Logic 0 for correct operation. CR5–CR4 RS1–RS0 Register Address Bits. These address bits are used to select which of the ADC’s registers are being select- ed during this serial interface communication. See Table 6. CR3 R/W A 0 in this bit location indicates that the next operation will be a write to a specified register. A 1 in this position indicates that the next operation will be 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, i.e., the contents of the data register are placed on the DOUT pin automatically when the SCLK pulses are applied. The commu- nications 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 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 will occur 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–CR0 CH1–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, i.e., 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 digi- tal conversion. Any change in channel resets the filter and a new conversion is started. Table 6. Register Selection RS1 RS0 Register Register Size 0 0 Communications Register during a Write Operation 8-Bit 0 0 Status Register during a Read Operation 8-Bit 0 1 Mode Register 8-Bit 1 0 Filter Register 8-Bit 1 1 Data Register 16-Bit Table 7. Channel Selection CH1 CH0 Channel 0 0 AIN(+) – AIN(–) 0 1 Reserved 1 0 AIN(–) – AIN(–) 1 1 VDD Monitor |
Аналогичный номер детали - AD7790BRM |
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Аналогичное описание - AD7790BRM |
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