Rainbow Electronics MAX1111 - Manual (Page 14)

MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
14 ______________________________________________________________________________________
SSTRB
CS
SCLK
DIN
DOUT
1 4 8 12 15 17
START
SEL2 SEL1 SEL0
UNI/
BIP
SGL/
DIF
PD1 PD0
B7 B6 B1 B0
t
ACQ
4µs (f
SCLK
= 500kHz)
IDLE
FILLED WITH
ZEROS
IDLE
CONVERSION
25µs TYP
A/D STATE
2 3 5 6 7 9 10 11 16 18
t
CONV
Figure 10. Internal Clock Mode Timing
PD0 CLOCK IN
t SSTRB
t CSH
t CONV
t SCK
SSTRB
SCLK
t
CSS
NOTE: FOR BEST NOISE PERFORMANCE, KEEP SCLK LOW DURING CONVERSION.
CS
Figure 11. Internal Clock Mode SSTRB Detailed Timing
Internal Clock
Internal clock mode frees the µP from the burden of
running the SAR conversion clock. This allows the con-
version results to be read back at the processor’s con-
venience, at any clock rate up to 2MHz. SSTRB goes
low at the start of the conversion and then goes high
when the conversion is complete. SSTRB is low for
25µs (typically), during which time SCLK should remain
low for best noise performance.
An internal register stores data when the conversion is
in progress. SCLK clocks the data out of this register at
any time after the conversion is complete. After SSTRB
goes high, the second falling clock edge produces the
MSB of the conversion at DOUT, followed by the
remaining bits in MSB-first format (Figure 10). CS does
not need to be held low once a conversion is started.
Pulling CS high prevents data from being clocked into
the MAX1110/MAX1111 and three-states DOUT, but it
does not adversely affect an internal clock-mode con-
version already in progress. When internal clock mode
is selected, SSTRB does not go into a high-impedance
state when CS goes high.
Figure 11 shows the SSTRB timing in internal clock
mode. In this mode, data can be shifted in and out of
the MAX1110/MAX1111 at clock rates up to 2MHz, pro-
vided that the minimum acquisition time, t
ACQ , is kept
above 1µs.