Datasheet AD7814 (Analog Devices) - 6

AD7814 CS t1 t t 7 2 SCLK 1 2 3 4 11 15 16 t3 t8 t4 LEADING DOUT ZERO DB9 DB8 DB0 t6 t5 DIN DON'T DON'T POWER- CARE CARE DOWN
Figure 2. Serial Interface Timing Diagram
Read Operation AD7814 to MC68HC11 Interface
Figure 2 shows the timing diagram for a serial read from the Figure 3 shows an interface between the AD7814 and the AD7814. The CS line enables the SCLK input. Ten bits of data MC68HC11 microcontroller. The MC68HC11 is configured in and a leading zero are transferred during a read operation. Read the master mode with its CPOL bit set to a logic one and its operations occur during streams of 16 clock pulses. The serial CPHA bit set to a logic one. When the MC68HC11 is config- data is accessed in a number of bytes if 10 bits of data are being ured like this, its SCLK line idles high between data transfers. read. At the end of the read operation, the DOUT line remains Data is transferred to and from the AD7814 in two 8-bit serial in the state of the last bit of data clocked out of the AD7814 data operations. The diagram shows the full (4-wire) interface. until CS returns high, at which time the DOUT line goes into PC1 of the MC68HC11 is configured as an output and used to three-state. drive the CS input.
Write Operation
Figure 2 also shows the timing diagram for a serial write to the
AD7814* MC68HC11*
AD7814. The write operation takes place at the same time as
SCLK SCLK
the read operation. Data is clocked into the control register on
DOUT MISO
the part on the rising edge of SCLK. Only the third bit in the data stream provides a user-controlled function. This third bit is
DIN MOSI
the power-down bit which, when set to a 1, puts the AD7814
CS PC1
into shutdown mode. The first 2 bits of the data stream are “don’t cares” while all other bits in the data stream, other than
*ADDITIONAL PINS OMITTED FOR CLARITY
the power-down bit, should be 0 to ensure correct operation of Figure 3. AD7814 to MC68HC11 Interface the AD7814. Data is loaded to the control register on the fif-
AD7814 to 8051 Interface
teenth falling SCLK edge and the data takes effect at this time An interface circuit between the AD7814 and the 8051 micro- (i.e., if the part is programmed to go into shutdown, it does so controller is shown in Figure 4. The 8xC51 is configured in its at this point). If the CS is brought high before this fifteenth SCLK Mode 0 serial interface mode. The serial clock line of the 8xC51 edge, the control register will not be loaded and the power-down (on P3.1) idles high between data transfers. Data is transferred status of the part will not change. to and from the AD7814 in two 8-bit serial data operations. The AD7814 outputs the MSB of its data stream as the first valid
MICROPROCESSOR INTERFACING
bit while the 8xC51 expects the LSB first. Thus, the data read The AD7814’s serial interface allows for easy interface to most into the serial buffer needs to be rearranged before the correct microcomputers and microprocessors. Figures 3 through 6 show data word from the AD7814 is available in the accumulator. some typical interface circuits. In the example shown, the AD7814 is connected to the serial The serial interface on the AD7814 consists of four wires: CS, port of the 8051. Because the serial interface of the 8xC51 con- DIN, DOUT, and SCLK. All interface circuits shown utilize all tains only one data line, the DIN line of the AD7814 is tied low four interface lines. However, it is possible to operate the inter- in the interface example given in Figure 4. face with three wires. If the application does not require the power-down facility offered by the AD7814, the DIN line can For applications that require the use of the power-down feature be tied permanently low. Thus, the interface can be operated of the AD7814, the serial interface should be implemented from just three wires: SCLK, CS, and DOUT. using data port lines on the 8051. This allows a full-duplex serial interface to be implemented. The method involves ‘bit- The serial data transfer to and from the AD7814 requires a banging’ a port line to generate a serial clock while using two 16-bit read operation. Many 8-bit microcontrollers have 8-bit other port lines to shift data in and out with the fourth port line serial ports and this 16-bit data transfer is handled as two 8-bit connecting to CS. Port lines 1.0 through 1.3 (with P1.1 config- transfers. Other microcontrollers and DSP processors transfer ured as an input) can be used to connect to SCLK, DOUT, 16 bits of data in a serial data operation. DIN, and CS, respectively, to implement this scheme. –6– REV. E Document Outline FEATURES FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS SPECIFICATIONS TIMING CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE PIN FUNCTION DESCRIPTIONS PIN CONFIGURATIONS CIRCUIT INFORMATION CONVERTER DETAILS TEMPERATURE VALUE REGISTER SERIAL INTERFACE Read Operation Write Operation MICROPROCESSOR INTERFACING AD7814 to MC68HC11 Interface AD7814 to 8051 Interface AD7814 to PIC16C6x/7x Interface AD7814 to ADSP-21xx Interface MOUNTING THE AD7814 SUPPLY DECOUPLING OUTLINE DIMENSIONS Revision History