MP3274
The MP3274 is easily interfaced to a wide variety of micropro-
cessors and other digital systems. Discussion of the timing re-
quirements of the MP3274 control signals will provide the sys-
tem designer with useful insight into the operation of the device.
2. ADEN = 0. At the falling edge of WR the data present at the
address is ignored and the channel selected during the pre-
vious conversion remains selected. In this case the track
andholdsettlingtimeisomittedandSTLnevergoeshigh. At
the rising edge of WR the input signal is sampled, and con-
version is started.
Figure 1. shows a complete timing diagram for the MP3274
convert start operation.
Therearetwopossiblestatesthatthedataoutputscouldbein
during a conversion.
Either WR or CS may be used to initiate a conversion. We
recommend using WR as used in Figure 1. It is quieter and has
less propagation delay than CS. If CS is used to trigger the con-
version the specified set-up times will be longer.
1. If RD is held high during a conversion the outputs would re-
main high impedance throughout the conversion. This is the
preferred method of operation as any noise present on the
data bus is rejected.
A conversion is started by taking WR low, then high again
(conversion is enabled on the rising edge of WR). There are two
possible conditions that will affect conversion timing.
2. If RD and CS are held low during a conversion, the data pre-
sent will be from the previous conversion until the present
conversion is completed when STS returns low. The data
from the new conversion will appear on the outputs. The
state of RD or CS should not change during a conversion.
1. ADEN = 1. At the falling edge of WR, the input channel is
determined by the data present on the address bits. The
track and hold begins to settle after which STL returns low,
indicating that the multiplexer and the buffer amp have set-
tled to less than 1/2 LSB of final value. If the rising edge of
WR returnshighpriortoSTLgoinglow, conversionwillbegin
onthefallingedgeofSTL. IftherisingedgeofWRisdelayed
until after STL returns low, the input signal is sampled and
the conversion is started at the rising edge of WR giving the
user better control of the sampling time.
Once a conversion is started and the STL or STS line goes
high, convert start commands will be ignored until the conver-
sion cycle is completed. The output data buffers cannot be en-
abled during conversion. In addition, all inputs and outputs
which change during conversion can introduce noise, and
should be avoided when possible.
Time
Interval
Tmin to
Tmax
Comments/Test Conditions
Limits
25°C
ADC Write Timing
ADC Control Timing
CS to WR Set-Up Time
CS to WR Hold Time
Address to WR Set-Up Time
Address to WR Hold Time
WR Pulse Width
t1
t2
t3
t4
t5
t6
0
0
0
0
80
0
0
0
0
80
ns min
ns min
ns min
ns min
ns min
ns min
ADEN to WR Set-Up Time
0
ADC Conversion Timing
WR to STL Delay
t7
150
150
ns max
Load ckt of Figure 5, CL = 20 pF,
ADEN = 1
STL High (mux/amp settle)
t8
t9
t12
t10
t13
t14
10
15
200
15
150
50
15
20
250
20
150
50
µs max
µs max
ns max
µs max
ns max
ns max
Load ckt of Figure 5, CL = 20 pF
Load ckt of Figure 5, CL = 20 pF
STL = 0 when ADEN = 0
STL to STS Low (Converting)
WR to STS High (ADEN = 0)
WR to STS Low (ADEN = 1)
STS High to Bus Relinquish Time
STS Low to Data Valid (RD = 0)
Load ckt of Figure 4
Load ckt of Figure 3, CL = 20 pF
Table 2. ADC Write Timing
(See Figure 1.)
Rev. 4.00
7
EXAR [ EXAR CORPORATION ]
