參數(shù)資料
型號(hào)： LM12L458CIV
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 模擬信號(hào)調(diào)理
英文描述： 12-Bit Sign Data Acquisition System with Self-Calibration
中文描述： SPECIALTY ANALOG CIRCUIT, PQCC44
封裝： PLASTIC, LCC-44
文件頁(yè)數(shù)： 17/36頁(yè)
文件大?。?/td> 695K
代理商： LM12L458CIV
Pin Description
V
A
+, V
D
+
Analog and digital supply voltage pins. The
LM12L458’s supply voltage operating range is
+3.0V to +5.5V. Accuracy is guaranteed only if
V
+ and V
+ are connected to the same power
supply. Each pin should have a parallel combi-
nation of 10 μF (electrolytic or tantalum) and
0.1 μF (ceramic) bypass capacitors connected
between it and ground.
D0–D15
The internal data input/output TRI-STATE buff-
ers are connected to these pins. These buffers
are designed to drive capacitive loads of 100 pF
or less. External buffers are necessary for driv-
ing higher load capacitances. These pins allows
the user a means of instruction input and data
output. With a logic
high
applied to the
BW
pin,
data lines D8–D15 are placed in a high imped-
ance state and data lines D0–D7 are used for in-
struction input and data output when the
LM12L458 is connected to an 8-bit wide data
bus. A logic
low
on the
BW
pin allows the
LM12L458 to exchange information over a 16-bit
wide data bus.
RD
Input for the active low READ bus control signal.
The data input/output TRI-STATE buffers, as se-
lected by the logic signal applied to the
BW
pin,
are enabled when RD and CS are both low. This
allows the LM12L458 to transmit information
onto the databus.
WR
Input for the active low WRITE bus control sig-
nal. The data input/output TRI-STATE buffers, as
selected by the logic signal applied to the
BW
pin, are enabled when WR and CS are both low.
This allows the LM12L458 to receive information
from the databus.
CS
Input for the active low Chip Select control sig-
nal. A logic low should be applied to this pin only
during a READ or WRITE access to the
LM12L458. The internal clocking is halted and
conversion stops while Chip Select is low. Con-
version resumes when the Chip Select input sig-
nal returns high.
ALE
Address Latch Enable input. It is used in sys-
tems containing a multiplexed databus. When
ALE is asserted
high
, the LM12L458 accepts in-
formation on the databus as a valid address. A
high-to-low transition will latch the address data
on A0–A4 and the logic state on the CS input.
Any changes onA0–A4 and CS whileALE is low
will not affect the LM12L458. See Figure 10
When a non-multiplexed bus is used, ALE is
continuously asserted
high
. See Figure 11
CLK
External clock input pin. The LM12L458 oper-
ates with an input clock frequency in the range of
0.05 MHz to 8 MHz.
A0–A4
The LM12L458’s address lines. They are used
to access all internal registers, Conversion
FIFO, and Instruction
RAM
.
SYNC
Synchronization input/output. When used as an
output, it is designed to drive capacitive loads of
100 pF or less. External buffers are necessary
for driving higher load capacitances. SYNC is an
input
if the Configuration register’s “I/O Select”
bit is
low
.Arising edge on this pin causes the in-
ternal S/H to hold the input signal. The next ris-
ing clock edge either starts a conversion or
makes a comparison to a programmable limit
depending on which function is requested by a
programming instruction. This pin will be an
out-
put
if “I/O Select” is set
high
. The SYNC output
goes high when a conversion or a comparison is
started and low when completed. (See Section
2.2). An internal reset after power is first applied
to the LM12L458 automatically sets this pin as
an input.
Bus Width input pin. This input allows the
LM12L458 to interface directly with either an 8-
or 16-bit databus. A logic high sets the width to 8
bits and places D8–D15 in a high impedance
state. A logic low sets the width to 16 bits.
Active low interrupt output. This output is de-
signed to drive capacitive loads of 100 pF or
less. External buffers are necessary for driving
higher load capacitances. An interrupt signal is
generated any time a non-masked interrupt con-
dition takes place. There are eight different con-
ditions that can cause an interrupt. Any interrupt
is reset by reading the Interrupt Status register.
(See Section 2.3.)
Active high Direct Memory Access Request out-
put. This output is designed to drive capacitive
loads of 100 pF or less. External buffers are nec-
essary for driving higher load capacitances. It
goes high whenever the number of conversion
results in the conversion FIFO equals a pro-
grammable value stored in the Interrupt Enable
register. It returns to a logic low when the FIFO is
empty.
Ground connection. It should be connected to a
low resistance and inductance analog ground re-
turn that connects directly to the system power
supply ground.
These are the eight analog inputs. A given chan-
nel is selected through the instruction RAM. Any
of the channels can be configured as an inde-
pendent single-ended input. Any pair of chan-
nels, whether adjacent or non-adjacent, can op-
erate as a fully differential pair.
This is the negative reference input. The
LM12L458 operates with 0V
≤
V
≤
V
.
This pin should be bypassed to ground with a
parallel combination of 10 μF and 0.1 μF (ce-
ramic) capacitors.
Positive reference input. The LM12L458 operate
with 0V
≤
V
≤
V
+. This pin should be by-
passed to ground with a parallel combination of
10 μF and 0.1 μF (ceramic) capacitors.
This is a no connect pin.
BW
INT
DMARQ
GND
IN0–IN7
V
REF
V
REF+
N.C.
www.national.com
17
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