AD7851
–26–
REV. B
Mode 2 (3-Wire SPI/QSPI Interface Mode)
Default Interface Mode
Figure 35 shows the timing diagram for Interface Mode 2 which
is the SPI/QSPI interface mode. Here the
SYNC input is active
low and may be pulsed or tied permanently low. If
SYNC is
permanently low, 16 clock pulses must be applied to the SCLK
pin for the part to operate correctly, and with a pulsed
SYNC
input a continuous SCLK may be applied provided
SYNC is
low for only 16 SCLK cycles. In Figure 35, the
SYNC going
low disables the three-state on the DOUT pin. The first falling
edge of the SCLK after the
SYNC going low clocks out the first
leading zero on the DOUT pin. The DOUT pin is three-stated
again a time t12 after the SYNC goes high. With the DIN pin,
the data input has to be set up a time t7 before the SCLK rising
edge as the part samples the input data on the SCLK rising edge
in this case. The POLARITY pin may be used to change the
SCLK edge which the data is sampled on and clocked out on. If
resetting the interface is required, the
SYNC must be taken high
and then low.
DB0
DB10
THREE-STATE
DB12
DB13
DB14
DB15
DB11
DB12
DB0
DB10
DB11
DB13
DB14
DB15
t
3 = –0.4 tCLKIN MIN (NONCONTINUOUS SCLK) ±0.4 tSCLK MIN/MAX (CONTINUOUS SCLK),
t
6 = 45ns MAX, t7 = 30ns MIN, t8 = 20ns MIN, t11 = 30ns MIN (NONCONTINUOUS SCLK),
30/0.4 t
SCLK = ns MIN/MAX (CONTINUOUS SCLK)
POLARITY PIN
LOGIC HIGH
SYNC (I/P)
16
234
5
16
SCLK (I/P)
t
9
t
5
t
11
t
3
t
10
t
12
DOUT (O/P)
t
8
DIN (I/P)
t
6
t
7
t
8
t
6
Figure 35. SPI/QSPI Mode 2 Timing Diagram for Read/Write Operation with DIN Input, DOUT Output, and
SYNC Input
(SM1 = SM2 = 0)
t
3 = –0.4 tCLKIN MIN (NONCONTINUOUS SCLK) ±0.4 tSCLK MIN/MAX (CONTINUOUS SCLK),
t
6 = 45ns MAX, t7 = 30ns MIN, t8 = 20ns MIN, t11 = 30ns MIN
DB0
DB10
THREE-STATE
DB12
DB13
DB14
DB15
DB11
DB12
DB0
DB10
DB11
DB13
DB14
DB15
POLARITY PIN
LOGIC HIGH
SYNC (I/P)
16
2345
16
SCLK (I/P)
t
9
t
5
t
11
t
3
t
10
t
12
DOUT (O/P)
t
8
DIN (I/P)
t
6
t
7
t
8
t
6
Figure 36. QSPI Mode 3 Timing Diagram for Read/Write Operation with
SYNC Input Edge Triggered (SM1 = 0, SM2 = 1)
Mode 3 (QSPI Interface Mode)
Figure 36 shows the timing diagram for Interface Mode 3. In
this mode, the DSP is the master and the part is the slave. Here
the
SYNC input is edge triggered from high to low, and the 16
clock pulses are counted from this edge. Because the clock
pulses are counted internally, the
SYNC signal does not have to
go high after the 16th SCLK rising edge as shown by the dotted
SYNC line. Thus a frame sync that gives a high pulse of one
SCLK cycle minimum duration at the beginning of the read/
write operation may be used. The rising edge of
SYNC enables
the three-state on the DOUT pin. The falling edge of
SYNC
disables the three-state on the DOUT pin, and data is clocked
out on the falling edge of SCLK. Once
SYNC goes high, the
three-state on the DOUT pin is enabled. The data input is
sampled on the rising edge of SCLK and thus has to be valid a
time t7 before this rising edge. The POLARITY pin may be
used to change the SCLK edge which the data is sampled on
and clocked out on. If resetting the interface is required, the
SYNC must be taken high and then low.