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AD7112 Fiches technique(PDF) 10 Page - Analog Devices |
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AD7112 Fiches technique(HTML) 10 Page - Analog Devices |
10 / 12 page AD7112 REV. 0 –10– MICROPROCESSOR INTERFACING Figures 18 to 20 show interfaces between the AD7112 and three popular 8-bit microprocessor systems, the MC68008, 8085A/8088 and the 8051. In the MC68008 and 8085/8088 in- terfaces, the AD7112 is memory mapped with separate ad- dresses for each DAC. AD7112-8085A/8088 INTERFACE Figure 18 shows a connection diagram for interfacing the AD7112 to both the 8085A and the 8088 microprocessors. This scheme is also suited to the Z80 microprocessor, but the Z80 address/data bus does not have to be demultiplexed. The AD7112 is memory mapped with separate memory addresses for DAC A and DAC B. 8085A / 8088 AD7112* CS WR DB7 – DB0 DATA BUS A15 – A8 AD7 – AD0 ALE ADDRESS BUS WR DEN DAC A / DAC B A** A+1** ADDRESS DECODE LOGIC 8-BIT LATCH * ANALOG CIRCUITRY HAS BEEN OMITTED FOR CLARITY. ** A = DECODED ADDRESS FOR AD7112 DAC A A+1 = DECODED ADDRESS FOR AD7112 DAC B Figure 18. AD7112–8085A/8088 Interface Circuit AD7112–68008 INTERFACE Figure 19 shows a connection diagram for interfacing the AD7112 to the 68008 microprocessor. The AD7112 is again memory mapped with separate memory addresses for DAC A and DAC B. AD7112* CS WR DB7 – DB0 DATA BUS ADDRESS BUS DAC A / DAC B A** A+1** ADDRESS DECODE LOGIC * ANALOG CIRCUITRY HAS BEEN OMITTED FOR CLARITY. ** A = DECODED ADDRESS FOR AD7112 DAC A A+1 = DECODED ADDRESS FOR AD7112 DAC B 68008 A23 – A1 D7 – D0 R /W AS DTACK Figure 19. AD7112–68008 Interface Circuit AD7112–8051 INTERFACE Figure 20 shows a connection diagram between the AD7112 and the 8051 microprocessor. The AD7112 is port mapped in this interface. The loading structure is as follows: Data to be loaded to the DAC is output to Port 1: P3.0, P3.1 and P3.2 are bit addressable port lines and are used to control the DAC select, CS and WR inputs. A sample routine for writing to DAC A is shown below. MOV A,DATA; Data to be written is loaded to the accumulator. CLR 3.2; Select DAC A. CLR 3.0; Bring CS low. CLR 3.1; Bring WR low. MOV A,P1; Write data to DAC. SET B 3.1; Deactivate WR. SET B 3.0; Deactivate CS 8051 P3.0 P3.1 P3.2 P1.0 P1.1 P1.2 P1.3 P1.4 P1.5 P1.6 P1.7 AD7112* CS WR DAC A / DAC B DB0 DB1 DB2 DB3 DB4 DB5 DB6 DB7 * ANALOG CIRCUITRY OMITTED FOR CLARITY Figure 20. AD7112–8051 Interface Circuit APPLICATIONS Automatic Gain Control In an automatic gain control system an input signal is attenuated or amplified so that its average output level remains constant. The AD7112 D/A converter is used here as a variable gain or at- tenuation element that adjusts the output signal relative to the input level. A feedback loop consisting of a detector, comparator, and up/ down counter continuously adjusts the contents of the counter and hence the gain or attenuation of the circuit so that the signal level at the output remains constant and equal to the reference input signal. The negative feedback action of the loop ensures that the average output voltage of the automatic gain control system remains constant. Figure 21 shows a block diagram of a typical AGC control loop using 1/2 AD7112 as the gain/ attenu- ation element. Whenever the input signal is outside the dynamic range of the programmable gain element in the AGC loop, there should be a stable, well defined input output relationship. |
Numéro de pièce similaire - AD7112 |
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Description similaire - AD7112 |
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