4.7.2 THE WEN PIN
A high level at this Write Enable input causes data to be writ-
ten into the capture buffer. One byte is written with the rise of
each sample clock. This input may go high asynchronously.
4.7.3 THE REN PIN
A high level at this Read Enable input causes data to be read
from the capture buffer. One byte is read with the rise of each
RCLK input. This signal should go high synchronous with the
RCLK input and should not be high while the WEN input is
high. If this input is high while the WEN input is high, the WEN
input has priority and the REN input is ignored, regardless of
which of these two inputs is high first. It is not possible to read
from the buffer while a write to the buffer is in progress.
4.7.4 THE ASW PIN
This Auto-Stop Write input has a dual function. With writing to
the buffer enabled and this ASW high, this pin acts as the
ASW (Auto-Stop Write) input, which causes writing to the
buffer to halt once the buffer is full (FF high). This prevents
write "wrap around" and the over-writing of older data. When
writing to the buffer is disabled, this pin is ignored. When the
device is in Test Mode, this pin acts as the Output Edge Select
input and functions as described for the OEDGE/TEN input.
4.7.5 THE BSIZE PINS
The two Buffer Size input pins (BSIZE0 and BSIZE1) are used
to select the required buffer size for the application or to by-
pass the buffer altogether. Refer to Section 8.0 USING THE
DATA BUFFER for use of these pins
5.0 PLL CONTROL: THE MULT PINS
The two MULT input pins (MULT0 and MULT1) are used to
select the CLK Multiplier for the internal PLL, or to bypass the
PLL. Refer to Section 7.0 CLOCK OPTIONS for more infor-
mation.
6.0 DIGITAL OUTPUT PINS
The ADC08B200 has 12 digital output pins: 8 Digital Data
Output pins, DRDY, WENSYNC, EF and FF
6.1 Digital Data Outputs
This 8-bit bus is LVTTL/LVCMOS compatible, with a Straight
Binary output format. Data is clocked out on this bus in one
of two ways. When the internal buffer is bypassed, data is
clocked out at the sample clock rate. When the internal buffer
is used, data is clocked out at the RCLK rate. In either case,
data is clocked out on the rising edge of the appropriate clock.
Refer to Section 7.0 CLOCK OPTIONS for information on
sample rate determination.
When the Capture Buffer is bypassed, data is read directly
from the converter at the sample clock rate.
When the capture buffer is used, data is read from the capture
buffer and presented at these pins when the REN input is
high. If OEDGE/TEN is high, the digital data output and DRDY
are held low when no valid data is being sent out. If OEDGE/
TEN is low, the digital data and DRDY are held high when no
valid data is being sent out. These pins source data at the
converter sample rate when the buffer is disabled.
Whether the buffer is enabled or not, the output data is pro-
vided synchronous with DRDY. That is, the data transition
occurs with the edge of DRDY defined by OEDGE/TEN such
that the data transitions on the rise of DRDY if OEDGE/TEN
is high or on the fall of DRDY if OEDGE/TEN is low.
The data output drivers are capable of sourcing and sinking
a relatively high current to enable rapid charging and dis-
charging of the output capacitance, thereby allowing fast
output rise and fall times. The data outputs should be as lightly
loaded as possible to minimize on-chip noise and the resulting
loss of SNR performance. Note the specified load capaci-
tance at the heading of the Electrical Characteristics Table.
6.2 The DRDY Pin
This output is intended for use to latch output data into a re-
ceiving device and transitions with the transition of the digital
data outputs. The synchronizing edge of the DRDY signal can
be selected with the OEDGE input. When the buffer is not
used, DRDY is active as long as the ADC is functioning. When
the buffer is enabled, DRDY is active only while data is being
sent out. When no valid data is being sent out, the DRDY
output sense is the opposite of the OEDGE input. When OE
is low and the device is NOT in the Test Pattern Mode
(OEDGE floating or at VA / 2), the DRDY output is in the high
impedance state, as are the data outputs. However, in Test
Pattern Mode the OE input is ignored and all output drivers
(data and DRDY) are in the active state. When the buffer is
used, DRDY is held low at all times except during the buffer
read phase, where it switches in synchronism with the data
output pins.
The DRDY output should be have a load that is identical to
the load of the digital data outputs to ensure that the DRDY
output edge transitions at the same time as does the data.
6.3 The WENSYNC Pin
This output is synchronous with the internal sample clock and
is provided as an indication as to when sampling takes place.
The actual point in time when sampling takes place is as in-
dicated in the "Capture and Write Enable" Timing Diagram.
6.4 The EF Pin
This Empty Flag goes high, synchronous with the internal
sample clock, when the Capture Buffer is empty, either by the
buffer having been completely read or upon RESET of the
device. This output goes low when one or more bytes is writ-
ten to the buffer. When EF goes high, the DRDY and Data
outputs stop switching and both DRDY and the Data lines re-
main low if OEDGE=1, or high if OEDGE=0.
6.5 The FF Pin
The Full Flag output indicates that the buffer is full and goes
high, synchronous with the internal sample clock, when the
capture buffer is full. If the WEN input remains high, the rise
of the next sample clock after the FF output goes high will
cause the buffer pointer to "wrap around" and start writing
over the previous data unless the ASW input is high. The FF
signal goes low when the REN signal goes high and the full
condition no longer exists. This signal also goes low upon a
RESET of the device.
7.0 CLOCK OPTIONS
The ADC08B200 incorporates a PLL to facilitate clocking.
The PLL, like any PLL or DLL, can add phase noise to the
clock signal and so to the conversion process. The effect of
this phase noise increases with higher analog signal input
frequencies. If a stable clock source at the desired sample
rate is available, it is preferable to use that clock as the sample
clock for the ADC08B200, bypassing the PLL. If such a source
is not available, the internal PLL may be used to multiply the
input clock frequency by 2, 4 or 8 to obtain the desired sample
rate from a lower frequency clock source.
Bypassing the PLL or setting the CLK frequency multiplier is
accomplished through the use of the two MULT pins as indi-
cated in Table 1. Expected noise performance with and with-
25 www.national.com
ADC08B200 / ADC08B200Q