PIN CONFIGURATION
Power-up Reset
+5VDC Supply (VLOGIC
)
1
2
28
27
26
25
24
23
22
21
20
19
18
17
16
15
Status
DB11 (MSB)
DB10
12/8
CS
Control
Logic
3
AO
4
DB9
Clock
R/C
5
DB8
CE
6
DB7
10V
Reference
12 Bits
+VCC
7
DB6
Ref Out
Analog Common
Ref In
8
DB5
12 Bits
12-Bit
D/A
9
DB4
Converter
10
11
12
13
14
DB3
Comparator
VEE
DB2
10kΩ
5kΩ
5kΩ
Bipolar Offset
10V Range
20V Range
DB1
DB0 (LSB)
Digital Common
CONTROLLING THE ADC674A
The Burr-Brown ADC674A can be easily interfaced to most
microprocessor systems and other digital systems. The mi-
croprocessor may take full control of each conversion, or the
converter may operate in a stand-alone mode, controlled
only by the R/C input. Full control consists of selecting an
8- or 112-bit conversion cycle, initiating the conversion, and
the output data when ready—choosing either 12 bits all at
once, or 8 bits followed by 4 bits in a left-justified format.
The five control inputs (12/8, CS, AO, R/C, and CE) are all
TTL-/CMOS-compatible. The functions of the control in-
puts are described in Table I. The control function truth table
is listed in Table II.
CE
CS
R/C
12/8
AO
OPERATION
0
X
↑
X
1
0
0
↓
X
X
0
0
0
0
↓
X
X
X
X
X
X
X
X
1
X
X
0
1
0
1
0
1
X
0
1
None
None
Initiate 12-bit conversion
Initiate 8-bit conversion
Initiate 12-bit conversion
Initiate 8-bit conversion
Initiate 12-bit conversion
Initiate 8-bit conversion
Enable 12-bit output
Enable 8 MSBs only
↑
1
1
1
1
1
1
1
↓
0
0
0
0
0
↓
1
1
1
0
0
Enable 4 LSBs plus 4
trailing zeros
TABLE II. Control Input Truth Table.
PIN
DESIGNATION
DEFINITION
FUNCTION
CE (Pin 6)
Chip Enable
(active high)
Must be high (“1”) to either initiate a conversion or read output data. 0-1 edge may be used to initiate a
conversion.
CS (Pin 3)
R/C (Pin 5)
Chip Select
(active low)
Must be low (“0”) ot either initiate a conversion or read output data. 1-0 edge may be used to initiate a conversion.
Read/Convert
(“1” = read)
Must be low (“0”) to initiate either 8- or 12-bit conversions. 1-0 edge may be used to initiate a conversion. Must be high
(“1”) to read output data. 0-1 edge may be used to initiate a read operation.
(“0” = convert)
AO (Pin 4)
Byte Address
Short Cycle
In the start-convert mode, AO selects 8-bit (A O = “1”) or 12-bit (AO = “0”) conversion mode. When reading output
data in two 8-bit bytes, AO = “0” accesses ±8MSBs (high byte) and AO = “1” accesses 4LSBs and trailing “0s” (low
byte).
12/8 (Pin 2)
Data Mode Select
(“1” = 12-bits)
When reading output data. 12/8 = “1” enables all 12 output bits simultaneously. 12/8 = “0” will enable the MSBs
or LSBs as determined by the AO line.
(“0” = 8-bits)
TABLE I. ADC674A Control Line Functions.
®
4
ADC674A
BB [ BURR-BROWN CORPORATION ]
