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AD7880BN Datasheet(PDF) 10 Page - Analog Devices |
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AD7880BN Datasheet(HTML) 10 Page - Analog Devices |
10 / 16 page AD7880 –10– REV. 0 a write operation starts a conversion. Data is read at the end of the conversion sequence as before. Figure 19 shows an example of initiating conversion using this method. A similar implemen- tation can be used for DSPs. Note that for all interfaces, a read operation should not be attempted during conversion. AD7880–MC68000 Interface An interface between the AD7880 and the MC68000 is shown in Figure 18. As before, conversion is initiated using an external timer. The AD7880 BUSY line can be used to interrupt the processor or, alternatively, software delays can ensure that con- version has been completed before a read to the AD7880 is at- tempted. Because of the nature of its interrupts, the 68000 requires additional logic (not shown in Figure 18) to allow it to be interrupted correctly. For further information on 68000 in- terrupts, consult the 68000 users manual. The MC68000 AS and R/W outputs are used to generate a separate RD input signal for the AD7880. CS is used to drive the 68000 DTACK input to allow the processor to execute a normal read operation to the AD7880. The conversion results are read using the following 68000 instruction: MOVE.W ADC, D0 where D0 is the 68000 D0 register where ADC is the AD7880 address A0 A15 D15 D0 ADDR DECODE ADDRESS BUS DATA BUS CONVST CS DB11 DB0 RD AD7880* MC68000 *ADDITIONAL PINS OMITTED FOR CLARITY R/W AS EN DTACK TIMER Figure 18. AD7880–MC68000 Interface AD7880–8086 Interface Figure 19 shows an interface between the AD7880 and the 8086 microprocessor. Unlike the previous interface examples, the microprocessor initiates conversion. This is achieved by gat- ing the 8086 WR signal with a decoded address output (differ- ent to the AD7880 CS address). Conversion is initiated and the result is read from the AD7880 using the following instruction: MOV AX, ADC where AX is the 8086 accumulator and where ADC is the AD7880 address AD15 AD0 ADDR DECODE ADDRESS BUS ADDRESS/DATA BUS CONVST CS DB11 DB0 RD AD7880* 8086 *ADDITIONAL PINS OMITTED FOR CLARITY WR RD LATCH ALE Figure 19. AD7880–8086 Interface AD7880–6809 Interface The AD7880 can also interface quite easily with 8-bit micro- processors. The 12-bit parallel data output from the AD7880 can be read into the microprocessor as an 8+4 byte structure. Figure 20 shows an interface to the MC6809 8-bit microproces- sor. As in previous cases, conversion is initiated using an exter- nal timer. At the end of conversion, BUSY triggers a one-shot which drives the IRQ interrupt input of the microprocessor. A double read is then performed to two unique addresses. The first read fetches the lower 8 bits (DB0–DB7) and loads the 74HC374 latch with the upper 4 bits (DB8–DB11). The sec- ond read fetches these upper 4 bits. A0 A15 D7 D0 ADDR DECODE ADDRESS BUS TIMER DATA BUS CONVST CS DB7 DB0 RD AD7880* MC6809 *ADDITIONAL PINS OMITTED FOR CLARITY R/W IRQ E BUSY ONE SHOT Q3 Q0 CLK D3 D0 74HC374 OE DB8 DB11 Figure 20. AD7880–6809 Interface |
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