AD7934-6_15 Datasheet, PDF (22/28 Pages) Analog Devices – 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer

AD7934-6
Reading Data from the AD7934-6
With the W/B pin tied logic high, the AD7934-6 interface
operates in word mode. In this case, a single read operation
from the device accesses the conversion data-word on Pin DB0
to Pin DB11. The DB8/HBEN pin assumes its DB8 function.
With the W/B pin tied to logic low, the AD7934-6 interface
operates in byte mode. In this case, the DB8/HBEN pin assumes
its HBEN function.
Conversion data from the AD7934-6 must be accessed in two
read operations with eight bits of data provided on DB0 to DB7
for each of the read operations. The HBEN pin determines
whether the read operation accesses the high byte or the low
byte of the 12-bit word. For a low byte read, DB0 to DB7
provide the eight LSBs of the 12-bit word. For a high byte read,
DB0 to DB3 provide the four MSBs of the 12-bit word. DB4 and
DB5 of the high byte provide the channel ID. DB6 and DB7 are
always 0. Figure 34 shows the read cycle timing diagram for a
12-bit transfer. When operated in word mode, the HBEN input
does not exist and only the first read operation is required to
access data from the device. When operated in byte mode, the
two read cycles shown in Figure 35 are required to access the
full data-word from the device.
The CS and RD signals are gated internally and the level is
triggered active low. In either word mode or byte mode, CS and
RD can be tied together as the timing specification t₁₀ and t₁₁ are
0 ns minimum. This means the bus is constantly driven by the
AD7934-6.
The data is placed onto the data bus a time, t13, after both CS
and RD go low. The RD rising edge can be used to latch data out
of the device. After a time, t14, the data lines become three-stated.
Alternatively, CS and RD can be tied permanently low, and the
conversion data is valid and placed onto the data bus a time, t9,
before the falling edge of BUSY.
Note that if RD is pulsed during the conversion time, this causes
a degradation in linearity performance of approximately 0.25
LSB. Reading during conversion by way of tying CS and RD low
does not cause any degradation.
HBEN/DB8
t₁₅
t₁₆
t₁₅
t₁₆
CS
RD
DB0 TO DB7
t₁₀
t₁₃
t₁₁
t₁₇
t₁₂
t₁₄
LOW BYTE
HIGH BYTE
Figure 35. AD7934-6 Parallel Interface—Read Cycle Timing for Byte Mode Operation (W/B = 0)
Rev. B | Page 22 of 28