AD7865AS-3 Analog Devices Inc, AD7865AS-3 Datasheet - Page 13

• Manufacturer Part Number: AD7865AS-3
• Description: IC ADC 14BIT 4CH 5V 44-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7865AS-3

• Rohs Status: RoHS non-compliant
• Number Of Bits: 14
• Sampling Rate (per Second): 350k
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 160mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-MQFP, 44-PQFP

REV. A
Accessing the Output Data Registers
There are four Output Data Registers, one for each of the four
possible conversion results from a conversion sequence. The
result of the first conversion in a conversion sequence is placed
in Register 1 and the second result is placed in Register 2 and
so on. For example if the conversion sequence V
V
results of the conversion on V
Registers 1 to 3 respectively. The Output Data register pointer
is reset to point to Register 1 at the end of the first conversion
in the sequence, just prior to EOC going low. At this point the
logic output FRSTDATA will go logic high to indicate that the
output data register pointer is addressing Register 1. When CS
and RD are both logic low the contents of the addressed regis-
ter are enabled onto the data bus (DB0–DB13).
When reading the output data registers after a conversion se-
quence, i.e., when BUSY goes low, the register pointer is incre-
mented on the rising edge of the RD signal as shown in Figure
8. However, when reading the conversion results between con-
versions in a conversion sequence the pointer will not be incre-
mented until a valid conversion result is in the register to be
addressed. In this case the pointer is incremented when the
conversion has ended and the result has been transferred to the
output data register. This happens when EOC goes low, there-
fore EOC may be used to enable the register contents onto the
CS
RD
IN4
*THE POINTER WILL NOT BE INCREMENTED BY A RISING EDGE ON RD UNTIL
THE CONVERSION RESULT IS IN THE OUTPUT DATA REGISTER. THE POINTER
IS RESET WHEN THE LAST CONVERSION RESULT IS READ
is selected (see Selecting a Conversion Sequence) the
COUNTER
POINTER*
RESET
2-BIT
Figure 8. Output Data Registers
FRSTDATA
CONVST
DECODE
DATA
BUSY
EOC
RD
CS
t
2
Figure 9. Timing Diagram, Reading After the Conversion Sequences
t
AD7865
OE #1
OE #2
OE #3
OE #4
DATA REGISTERS
1
IN1
, V
OUTPUT
NOT VALID
IN3
t
BUSY
and V
(V
(V
(V
IN1
IN3
IN4
)
)
)
IN4
IN1
DRIVERS
V
are placed in
DRIVE
, V
O/P
OE
FRSTDATA
IN3
V
DB0 TO
DB13
IN1
and
t
6
t
10
–13–
V
IN2
data bus as described in Reading Between Conversions in the
Conversion Sequence. The pointer is reset to point to Register 1
on the rising edge of the RD signal when the last conversion
result in the sequence is being read. In the example shown in
Figure 8, this means that the pointer is set to Register 1 when
the contents of Register 3 are read.
Reading After the Conversion Sequence
Figure 9 shows the same conversion sequence as Figure 7. In
this case, however, the results of the four conversions (on V
to V
BUSY goes logic low. The FRSTDATA signal goes logic high
at the end of the first conversion just prior to EOC going logic
low. As mentioned previously FRSTDATA has an indetermi-
nate state after initial power up, therefore FRSTDATA may
already be logic high. Unlike the case when reading during a
conversion the output data register pointer is incremented on
the rising edge of RD because the next conversion result is
available in this case. This means FRSTDATA will go logic low
after the first rising edge on RD.
Successive read operations will access the remaining conversion
results in ascending channel order. Each read operation incre-
ments the output data register pointer. The read operation that
accesses the last conversion result causes the output data regis-
ter pointer to be reset so that the next read operation will access
the first conversion result again. This is shown in Figure 8 with
the fifth read after BUSY goes low accessing the result of the
conversion on V
circular buffer in which the conversion results may be continu-
ally accessed. The FRSTDATA signal will go high when the
first conversion result is available.
Data is enabled onto the data bus DB0 to DB13 using CS and
RD. Both CS and RD have the same functionality as described
in the previous section. There are no restrictions or performance
implications associated with the position of the read operations
after BUSY goes low, however there is a minimum time be-
tween read operations that must be adhered to. Notice also that a
“Quiet Time” is needed before the start of the next conversion
sequence.
t
3
t
8
t
7
IN4
V
) are read after all conversions have finished, i.e., when
IN3
t
4
IN1
V
IN4
. Thus the output data registers acts as a
t
10
QUIET
TIME
V
IN1
AD7865
IN1