Datasheet

AD7654
Rev. B | Page 19 of 28
t
1
t
3
t
4
t
17
BUSY
DATA
BUS
t
16
NEW A
OR B
PREVIOUS CHANNEL A
OR B
PREVIOUS CHANNEL B
OR NEW A
t
10
CS = RD = 0
EOC
CNVST
03057-024
Figure 24. Master Parallel Data Timing for Continuous Read
Slave Parallel Interface
In slave parallel reading mode, the data can be read either after
each conversion, which is during the next acquisition phase or
during the other channel’s conversion, or during the following
conversion, as shown in
Figure 25 and Figure 26, respectively.
When the data is read during the conversion, however, it is
recommended that it is read only during the first half of the
conversion phase. This avoids any potential feedthrough
between voltage transients on the digital interface and the most
critical analog conversion circuitry.
DATA BUS
t
18
t
19
BUSY
CURRENT
CONVERSION
CS
RD
03057-025
Figure 25. Slave Parallel Data Timing for a Read After Conversion
PREVIOUS
CONVERSION
t
1
t
3
t
18
t
19
t
4
BUSY
DATA BUS
t
13
t
11
t
12
t
10
CS =0
EOC
CNVST, RD
03057-026
Figure 26. Slave Parallel Data Timing for a Read During Conversion
8-Bit Interface (Master or Slave)
The BYTESWAP pin allows a glueless interface to an 8-bit bus.
As shown in
Figure 27, the LSB byte is output on D[7:0] and the
MSB is output on D[15:8] when BYTESWAP is low. When
BYTESWAP is high, the LSB and MSB bytes are swapped, the
LSB is output on D[15:8], and the MSB is output on D[7:0]. By
connecting BYTESWAP to an address line, the 16-bit data can
be read in two bytes on either D[15:8] or D[7:0].
BYTESWAP
PINS D[15:8]
PINS D[7:0]
HI-Z
HI-Z
HIGH BYTE LOW BYTE
LOW BYTE HIGH BYTE
HI-Z
HI-Z
t
18
t
18
t
19
CS
RD
03057-027
Figure 27. 8-Bit Parallel Interface
Channel A/
B
Output
The A/
B
input controls which channel’s conversion results
(INAx or INBx) are output on the data bus. The functionality
of A/
B
is detailed in Figure 28. When high, the data from
Channel A is available on the data bus. When low, the data from
Channel B is available on the bus. Note that Channel A can be
read immediately after conversion is done (
EOC
), while
Channel B is still in its converting phase. However, in any of the
serial reading modes, Channel A data is updated only after
Channel B is converted.
t
18
t
20
CS
DATA BUS
RD
HI-Z
A/B
HI-Z
CHANNEL A
CHANNEL B
03057-028
Figure 28. A/
B
Channel Reading