參數(shù)資料
型號: AD7874SQ
廠商: ANALOG DEVICES INC
元件分類: ADC
英文描述: LC2MOS 4-Channel, 12-Bit Simultaneous Sampling Data Acquisition System
中文描述: 4-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, CDIP28
封裝: 0.600 INCH, HERMETIC SEALED, CERDIP-28
文件頁數(shù): 11/16頁
文件大?。?/td> 414K
代理商: AD7874SQ
AD7874
REV. C
–11–
Some applications may require that the conversion is initiated
by the microprocessor rather than an external timer. One option
is to decode the AD7874
CONVST
from the address bus so
that a write operation starts a conversion. Data is read at the
end of the conversion sequence as before. Figure 16 shows an
example of initiating conversion using this method. Note that
for all interfaces, a read operation should not be attempted dur-
ing conversion.
AD7874–MC68000 Interface
An interface between the AD7874 and the MC68000 is shown
in Figure 15. As before, conversion is initiated using an external
timer. T he AD7874
INT
line can be used to interrupt the pro-
cessor or, alternatively, software delays can ensure that conver-
sion has been completed before a read to the AD7874 is
attempted. Because of the nature of its interrupts, the 68000
requires additional logic (not shown in Figure 15) to allow it to
be interrupted correctly. For further information on 68000 in-
terrupts, consult the 68000 users manual.
T he MC68000
AS
and R/
W
outputs are used to generate a
separate
RD
input signal for the AD7874.
CS
is used to drive
the 68000
DTACK
input to allow the processor to execute a
normal read operation to the AD7874. T he conversion results
are read using the following 68000 instruction:
MOVE.W ADC,D0
where D0 is the 68000 D0 register and
ADC is the AD7874 address.
A0
A15
D15
D0
ADDR
DECODE
ADDRESS BUS
DATA BUS
CONVST
CS
DB11
DB0
RD
AD7874*
MC68000
*ADDITIONAL PINS OMITTED FOR CLARITY
R/W
AS
EN
DTACK
TIMER
Figure 15. AD7874–MC68000 Interface
AD7874–8086 Interface
Figure 16 shows an interface between the AD7874 and the 8086
microprocessor. Unlike the previous interface examples, the
microprocessor initiates conversion. T his is achieved by gating
the 8086
WR
signal with a decoded address output (different to
the AD7874
CS
address). T he AD7874
INT
line is used to in-
terrupt the microprocessor when the conversion sequence is
completed. Data is read from the AD7874 using the following
instruction:
MOV AX ,ADC
where AX is the 8086 accumulator and
ADC is the AD7874 address.
ALE
AD15
AD0
ADDR
DECODE
ADDRESS BUS
ADDRESS/DATA BUS
CONVST
CS
DB11
DB0
RD
AD7874*
8086
*ADDITIONAL PINS OMITTED FOR CLARITY
WR
RD
LATCH
Figure 16. AD7874–8086 Interface
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