
REV. B
–24–
AD7853/AD7853L
DETAILED TIMING SECTION
Mode 1 (2-Wire 8051 Interface)
The read and writing takes place on the DIN line and the con-
version is initiated by pulsing the
CONVST
pin (note that in
every write cycle the 2/
3
Mode bit must be set to 1). The con-
version may be started by setting the
CONVST
bit in the con-
trol register to 1 instead of using the
CONVST
line.
Below in Figure 33 and in Figure 34 are the timing diagrams for
Interface Mode 1 in Table X where we are in the 2-wire inter-
face mode. Here the DIN pin is used for both input and output
as shown. The
SYNC
input is level triggered active low and can
be pulsed (Figure 33) or can be constantly low (Figure 34).
In Figure 33 the part samples the input data on the rising edge
of SCLK. After the 16th rising edge of SCLK the DIN is con-
figured as an output. When the
SYNC
is taken high the DIN is
three-stated. Taking
SYNC
low disables the three-state on the
DIN pin and the first SCLK falling edge clocks out the first data
bit. Once the 16 clocks have been provided the DIN pin will
automatically revert back to an input after a time t
14
. Note that a
continuous SCLK shown by the dotted waveform in Figure 33
can be used provided that the
SYNC
is low for only 16 clock
pulses in each of the read and write cycles. The POLARITY pin
may be used to change the SCLK edge which the data is sampled
on and clocked out on.
In Figure 34 the
SYNC
line is tied low permanently and this
results in a different timing arrangement. With
SYNC
tied low
permanently the DIN pin will never be three-stated. The 16th
rising edge of SCLK configures the DIN pin as an input or an
output as shown in the diagram. Here no more than 16 SCLK
pulses must occur for each of the read and write operations.
If reading from and writing to the calibration registers in this
interface mode, all the selected calibration registers must be
read from or written to. The read and write operations cannot
be aborted. When reading from the calibration registers, the
DIN pin will remain as an output for the full duration of all the
calibration register read operations. When writing to the calibra-
tion registers, the DIN pin will remain as an input for the full
duration of all the calibration register write operations.
SCLK (I/P)
SYNC
(I/P)
t
3
t
8
DIN (I/O)
DB15
DB0
DB0
t
3
t
11
t
6
POLARITY PIN
LOGIC HIGH
1
16
16
1
t
5A
t
12
DIN BECOMES AN INPUT
DB15
THREE-STATE
DATA READ
DATA WRITE
t
7
t
6
t
14
t
11
DIN BECOMES AN OUTPUT
t
3
= –0.4 t
MIN (NONCONTINUOUS SCLK) –/+0.4 t
MIN/MAX (CONTINUOUS SCLK),
t
6
= 75/115 MAX (5V/3V), t
7
= 40/60ns
MIN (5V/3V), t
8
= 20/30
MIN (5V/3V)
Figure 33. Timing Diagram for Read/Write Operation with DIN as an Input/Output (i.e., Interface Mode 1, SM1 = SM2 = 0)
SCLK (I/P)
t
8
DIN (I/O)
DB15
DB0
DB0
t
6
1
16
16
1
DIN BECOMES AN INPUT
DB15
DATA READ
DATA WRITE
t
7
t
6
t
14
t
6
= 75/115 MAX (5V/3V), t
7
= 40/60ns
MIN (5V/3V), t
8
= 20/30
MIN (5V/3V),
t
13
= 90/130 MAX (5V/3V), t
14
= 50/90ns
MAX (5V/3V)
6
t
13
POLARITY PIN
LOGIC HIGH
Figure 34. Timing Diagram for Read/Write Operation with DIN as an Input/Output and
SYNC
Input Tied Low
(i.e., Interface Mode 1, SM1 = SM2 = 0)