Rainbow Electronics MAX1143 - Manual (Page 11)

MAX1142/MAX1143
14-Bit ADC, 200ksps, +5V Single-Supply
with Reference
______________________________________________________________________________________ 11
In external clock mode, SSTRB is high-impedance
when
CS is high. In external clock mode, CS is normally
held low during the entire conversion. If CS goes high
during the conversion, SCLK is ignored until CS goes
low. This allows external clock mode to be used with 8-
bit bytes.
Internal Clock
In internal clock mode, the MAX1142/MAX1143 gener-
ates its own conversion clock. This frees the micro-
processor from the burden of running the SAR conver-
sion clock, and allows the conversion results to be read
back at the processor’s convenience, at any clock rate
up to 8MHz.
SSTRB goes low at the start of the conversion and goes
high when the conversion is complete. SSTRB will be
low for a maximum of 6µs, during which time SCLK
should remain low for best noise performance. An inter-
nal register stores data when the conversion is in
progress. SCLK clocks the data out of the internal stor-
age register at any time after the conversion is com-
plete.
The MSB of the conversion is available at DOUT when
SSTRB goes high. The subsequent 15 falling edges on
SCLK shift the remaining bits out of the internal storage
register (Figure 4).
CS does not need to be held low
once a conversion is started.
When internal clock mode is selected, SSTRB does not
go into a high-impedance state when
CS goes high.
Figure 5 shows the SSTRB timing in internal clock
mode. In internal clock mode, data can be shifted into
the MAX1142/MAX1143 at clock rates up to 4.8MHz,
provided that the minimum acquisition time,
t
ACQ , is kept above 1.14µs in bipolar mode and 1.82µs
in unipolar-mode. Data can be clocked out at 8MHz.
Output Data
The output data format is straight binary for unipolar
conversions and two’s complement in bipolar mode. In
both modes the MSB is shifted out of the MAX1142/
MAX1143 first.
Table 2. User-Programmable Outputs
OUTPUT
PIN
PROGRAMMED
THROUGH
CONTROL-
BYTE
POWER-ON
OR RST
DEFAULT
DESCRIPTION
P2 Bit 2 0
P1 Bit 1 0
P0 Bit 0 0
U ser p r og r am m ab l e outp uts fol l ow the state of the C ontr ol - Byte’ s thr ee LS Bs,
and ar e up d ated si m ul taneousl y w hen a new C ontr ol - Byte i s w r i tten. O utp uts
ar e p ush- p ul l . In har d w ar e and softw ar e shutd ow n, these outp uts ar e
unchang ed and r em ai n l ow - i m p ed ance.
ACQUISITION CONVERSION IDLE IDLE
SCLK
DOUT
A/D
STATE
DIN
SSTRB
CS
4 1 8 12
START M1 M0 P2 P1 P0
UNI/
BIP
INT/
EXT
15 21 24
B10 B9 B12 B11 B8 B7 B2
B13
MSB
B0
LSB
FILLED WITH
ZEROS B1 X X
t ACQ
Figure 2. Short Acquisition Mode (24-Clock Cycles) External Clock, Bipolar Mode