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参数资料
型号： LM12458CIVF/NOPB
厂商： NATIONAL SEMICONDUCTOR CORP
元件分类： 模拟信号调理
英文描述： SPECIALTY ANALOG CIRCUIT, PQFP44
封装： PLASTIC, QFP-44
文件页数： 15/36页
文件大小： 1195K
代理商： LM12458CIVF/NOPB
Pin Descriptions
V
A+VD+ Analog
and digital supply voltage pins. The
LM12(H)454/8’s supply voltage operating range is
+3.0V to +5.5V. Accuracy is guaranteed only if
V
A+ and VD+ are connected to the same power
supply. Each pin should have a parallel combina-
tion of 10 F (electrolytic or tantalum) and 0.1 F
(ceramic) bypass capacitors connected between it
and ground.
D0–D15 The internal data input/output TRI-STATE buffers
are connected to these pins. These buffers are
designed to drive capacitive loads of 100 pF or
less. External buffers are necessary for driving
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 impedance state and
data lines D0–D7 are used for instruction input
and data output when the LM12(H)454/8 is con-
nected to an 8-bit wide data bus. A logic low on
the BW pin allows the LM12(H)454/8 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 LM12(H)454/8 to transmit information
onto the data bus.
WR
Input for the active low WRITE 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 WR and CS are both low. This
allows the LM12(H)454/8 to receive information
from the data bus.
CS
Input for the active low Chip Select control signal.
A logic low should be applied to this pin only
during
a
READ
or
WRITE
access
to
the
LM12(H)454/8. The internal clocking is halted and
conversion stops while Chip Select is low. Conver-
sion resumes when the Chip Select input signal
returns high.
ALE
Address Latch Enable input. It is used in systems
containing a multiplexed data bus. When ALE is
asserted high, the LM12(H)454/8 accepts infor-
mation on the data bus as a valid address. A
high-to-low transition will latch the address data on
A0–A4 while the CS is low. Any changes on
A0–A4 and CS while ALE is low will not affect the
LM12(H)454/8. See Figure 10. When a non-
multiplexed bus is used, ALE is continuously as-
serted high. See Figure 11.
CLK
External clock input pin. The LM12(H)454/8 oper-
ates with an input clock frequency in the range of
0.05 MHz to 10.0 MHz.
A0–A4
The LM12(H)454/8’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 in-
put if the Configuration register’s “I/O Select” bit is
low. A rising edge on this pin causes the internal
S/H to hold the input signal. The next rising clock
edge either starts a conversion or makes a com-
parison to a programmable limit depending on
which function is requested by a programming
instruction. This pin will be an output if “I/O Se-
lect” 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 inter-
nal reset after power is first applied to the
LM12(H)454/8 automatically sets this pin as an
input.
BW
Bus Width input pin. This input allows the
LM12(H)454/8 to interface directly with either an
8- or 16-bit data bus. 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.
INT
Active low interrupt output. This output is designed
to drive capacitive loads of 100 pF or less. Exter-
nal buffers are necessary for driving higher load
capacitances. An interrupt signal is generated any
time a non-masked interrupt condition takes place.
There are eight different conditions that can cause
an interrupt. Any interrupt is reset by reading the
Interrupt Status register. (See Section 2.3.)
DMARQ 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 program-
mable value stored in the Interrupt Enable regis-
ter. It returns to a logic low when the FIFO is
empty.
GND
LM12(H)454/8 ground connection. It should be
connected to a low resistance and inductance
analog ground return that connects directly to the
system power supply ground.
IN0–IN7
(IN0–IN3
LM12H454
LM12454)
The eight (LM12(H)458) or four (LM12454)
analog inputs. A given channel is selected
through the instruction RAM. Any of the chan-
nels can be configured as an independent
single-ended input. Any pair of channels,
whether adjacent or non-adjacent, can operate
as a fully differential pair.
S/H IN+
S/H IN
The LM12454’s non-inverting and inverting
inputs to the internal S/H.
MUXOUT+
MUXOUT
The LM12454’s non-inverting and inverting
outputs from the internal multiplexer.
V
REF
The
negative
reference
input.
The
LM12(H)454/8 operate with 0V
≤ V
REF
≤
V
REF+.
This pin should be bypassed to
ground with a parallel combination of 10 F
and 0.1 F (ceramic) capacitors.
V
REF+
The
positive
reference
input.
The
LM12(H)454/8 operate with 0V
≤ V
REF+
≤
V
A+. This pin should be bypassed to ground
with a parallel combination of 10 F and
0.1 F (ceramic) capacitors.
V
REFOUT
The internal 2.5V bandgap’s output pin. This
pin should be bypassed to ground with a 100
F capacitor.
LM12454/LM12458/LM12H458
www.national.com
22
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