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AD7891BP-1 Datasheet(PDF) 9 Page - Analog Devices |
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AD7891BP-1 Datasheet(HTML) 9 Page - Analog Devices |
9 / 20 page AD7891 –9– REV. A SERIAL INTERFACE MODE FUNCTIONS When the part is configured for serial mode (MODE = 0), five of the 12 data input/output lines provide serial interface functions. These functions are outlined below. Mnemonic Description SCLK Serial Clock Input. This is an externally applied serial clock which is used to load serial data to the control register and to access data from the output register. TFS Transmit Frame Synchronization Pulse. Active low logic input with serial data expected after the falling edge of this signal. RFS Receive Frame Synchronization Pulse. This is an active low logic input with RFS provided externally as a strobe or framing pulse to access serial data from the output register. For applications that require that data be transmitted and received at the same time, RFS and TFS should be connected together. DATA OUT Serial Data Output. Sixteen bits of serial data are provided with the data FORMAT bit and the three address bits of the control register preceding the 12 bits of conversion data. Serial data is valid on the falling edge of SCLK for sixteen edges after RFS goes low. Output conversion data coding is twos comple- ment when the FORMAT Bit of the control register is 1 and straight binary when the FORMAT Bit of the control register is 0. DATA IN Serial Data Input. Serial data to be loaded to the control register is provided at this input. The first six bits of serial data are loaded to the control register on the first six falling edges of SCLK after TFS goes low. Serial data on subsequent SCLK edges is ignored while TFS remains low. TEST Test Pin. When the device is configured for serial mode of operation, two of the pins which had been data inputs become test inputs. To ensure correct operation of the device, both TEST inputs should be tied to a logic low potential. CONTROL REGISTER The control register for the AD7891 contains 6 bits of information as described below. These 6 bits can be written to the control register either in a parallel mode write operation or via a serial mode write operation. The default (power-on) condition of all bits in the control register is 0. Six serial clock pulses must be provided to the part in order to write data to the control register. If TFS re- turns high before six serial clock cycles then no data transfer takes place to the control register and the write cycle will have to be restarted to write data to the control register. However, if the SWCONV bit of the register was previously set to a logic 1 and TFS is brought high before six serial clock cycles, then another conversion will be initiated. B S M 2 A1 A0 AV N O C W SY B T S W ST A M R O F A2 Address Input. This input is the most significant address input for multiplexer channel selection. A1 Address Input. This is the second most significant address input for multiplexer channel selection. A0 Address Input. Least significant address input for multiplexer channel selection. When the address is written to the control register, an internal pulse is initiated to allow for the multiplexer settling time and track/hold acquisi- tion time before the track/hold goes into hold and conversion is initiated. When the internal pulse times out, the track/hold goes into hold and conversion is initiated. The selected channel is given by the formula: A2 × 4 + A1 × 2 + A0 + 1 SWCONV Conversion Start. Writing a 1 to this bit initiates a conversion in a similar manner to the CONVST input. Con- tinuous conversion starts do not take place when there is a 1 in this location. The internal pulse and the conver- sion process are initiated when a 1 is written to this bit. With a 1 in this bit, the hardware conversion start, i.e., the CONVST input, is disabled. Writing a 0 to this bit enables the hardware CONVST input. SWSTBY Standby Mode Input. Writing a 1 to this bit places the device in its standby or power-down mode. Writing a 0 to this bit places the device in its normal operating mode. FORMAT Data Format. Writing a 0 to this bit sets the conversion data output format to straight (natural) binary. This data format is generally be used for unipolar input ranges. Writing a 1 to this bit sets the conversion data output format to twos complement. This output data format is generally used for bipolar input ranges. |
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