参数资料
型号: HI1-574ALD-5
厂商: HARRIS SEMICONDUCTOR
元件分类: ADC
英文描述: Complete, 12-Bit A/D Converters with Microprocessor Interface
中文描述: 12-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, CDIP28
文件页数: 14/18页
文件大小: 200K
代理商: HI1-574ALD-5
6-965
“Stand-Alone Operation”
The simplest control interface calls for a singe control line
connected to R/C. Also, CE and 12/8 are wired high, CS and
A
O
are wired low, and the output data appears in words of
12 bits each.
The R/C signal may have any duty cycle within (and
including) the extremes shown in Figures 8 and 9. In gen-
eral, data may be read when R/C is high unless STS is also
high, indicating a conversion is in progress. Timing parame-
ters particular to this mode of operation are listed below
under “Stand-Alone Mode Timing”.
Conversion Length
A Convert Start transition (see Table 1) latches the state of
A
O
, which determines whether the conversion continues for
12 bits (A
O
low) or stops with 8 bits (A
O
high). If all 12 bits are
read following an 8-bit conversion, the last three LSBs will
read ZERO and DB3 will read ONE. A
O
is latched because it
is also involved in enabling the output buffers (see “Reading
the Output Data”). No other control inputs are latched.
Conversion Start
A conversion may be initiated as shown in Table 1 by a logic
transition on any of three inputs: CE, CS or R/C. The last of
the three to reach the correct state starts the conversion, so
one, two or all three may be dynamically controlled. The
nominal delay from each is the same, and if necessary, all
three may change state simultaneously. However, to ensure
that a particular input controls the start of conversion, the
other two should be set up at least 50ns earlier. See the
HI-774 Timing Specifications, Convert Mode.
This variety of HI-X74(A) control modes allows a simple
interface in most system applications. The Convert Start
timing relationships are illustrated in Figure 4.
The output signal STS indicates status of the converter by
going high only while a conversion is in progress. While STS
is high, the output buffers remain in a high impedance state
and data cannot be read. Also, an additional Start Convert
will not reset the converter or reinitiate a conversion while
STS is high.
Reading the Output Data
The output data buffers remain in a high impedance state
until four conditions are met: R/C high, STS low, CE high and
CS low. At that time, data lines become active according to
the state of inputs 12/8 and A
O
. Timing constraints are
illustrated in Figure 5.
HI-574A STAND-ALONE MODE TIMING
SYMBOL
PARAMETER
MIN
TYP
MAX
UNITS
t
HRL
Low R/C Pulse Width
50
-
-
ns
t
DS
STS Delay from R/C
-
-
200
ns
t
HDR
Data Valid after R/C Low
25
-
-
ns
t
HS
STS Delay after Data Valid
300
-
1200
ns
t
HRH
High R/C Pulse Width
150
-
-
ns
t
DDR
Data Access Time
-
-
150
ns
Time is measured from 50% level of digital transitions. Tested with a
50pF and 3k
load.
HI-674A STAND-ALONE MODE TIMING
SYMBOL
PARAMETER
MIN
TYP
MAX
UNITS
t
HRL
Low R/C Pulse Width
50
-
-
ns
t
DS
STS Delay from R/C
-
-
200
ns
t
HDR
Data Valid after R/C Low
25
-
-
ns
t
HS
STS Delay after Data Valid
25
-
850
ns
t
HRH
High R/C Pulse Width
150
-
-
ns
t
DDR
Data Access Time
-
-
150
ns
Time is measured from 50% level of digital transitions. Tested with a
50pF and 3k
load.
HI-774 STAND-ALONE MODE TIMING
SYMBOL
PARAMETER
MIN
TYP
MAX
UNITS
t
HRL
Low R/C Pulse Width
50
-
-
ns
t
DS
STS Delay from R/C
-
-
200
ns
t
HDR
Data Valid after R/C Low
20
-
-
ns
t
HS
STS Delay after Data Valid
-
-
850
ns
t
HRH
High R/C Pulse Width
150
-
-
ns
t
DDR
Data Access Time
-
-
150
ns
TABLE 1. TRUTH TABLE FOR HI-X74(A) CONTROL INPUTS
CE
CS
R/C
12/8
A
O
OPERATION
0
X
X
X
X
None
X
1
X
X
X
None
0
0
X
0
Initiate 12-bit conversion
0
0
X
1
Initiate 8-bit conversion
1
0
X
0
Initiate 12-bit conversion
1
0
X
1
Initiate 8-bit conversion
1
0
X
0
Initiate 12-bit conversion
1
0
X
1
Initiate 8-bit conversion
1
0
1
1
X
Enable 12-bit Output
1
0
1
0
0
Enable 8 MSBs Only
1
0
1
0
1
Enable 4 LSBs Plus 4 Trailing
Zeroes
HI-574A, HI-674A, HI-774
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