900,000+ datasheet pdf search and download

Datasheet4U offers most rated semiconductors data sheet pdf






Philips

AN426 Datasheet Preview

AN426 Datasheet

Controlling Air Core Meters

No Preview Available !

Philips Semiconductors
www.datasheet4u.com
Controlling air core meters with the 87C751 and SA5775
Application note
AN426
INTRODUCTION
Often, certain classes of microcontroller
applications surface where large amounts of
on-chip resources such as a large program
memory space and numerous I/O pins are
not required. These applications are typically
cost sensitive and desirable attributes of the
MCU include low cost and modest on-chip
resources such as program and data
memory, I/O, and timer-counters. Substantial
benefits of reduced design cycle time can be
realized by using an industry-standard
architecture having software compatibility
with existing popular microcontrollers.
THE 87C751
The Philips 87C751 is one such
microcontroller that easily meets these
requirements. This device, shown in Figure 1,
has a 2k x 8 program memory, 64 bytes of
RAM, 19 parallel I/O lines, and a 16-bit
autoreload timer-counter. It also includes an
I2C serial interface and a fixed rate timer. The
87C751 is based on the 80C51 core and thus
uses an industry-standard architecture and
instruction set. The device is available in both
ROM (83C751) and EPROM (87C751)
versions. The EPROM version is available in
both UV erasable and OTP packages.
References to the 87C751 in this document
also apply to the 83C751, unless explicitly
stated.
TYPICAL APPLICATION
A typical example of such an application is
the interface between the 87C751 and the
Philips SA5775 Serial Gauge Driver, SGD,
shown in Figure 2. This circuit includes the
87C751 microcontroller, the SA5775 Serial
Gauge Driver, an NE555 timer, and discrete
support components.
An air core meter differs from a conventional
(d’Arsonval) meter movement in that it has no
spring to return the needle to a
predetermined position, no zeroing
adjustment, and no permanent magnet in the
classical sense. Instead, it consists of two
coils of wire wound in quadrature with each
other around a central core in which there is
a disc magnetized along its diameter. A shaft
is placed through the center of this disc so
that the shaft rotates with the disc. An
indicating needle attached to this shaft will
rotate with it.
SA5775 Serial Gauge Driver
The SA5775 is a monolithic driver for
controlling air core meters typically used in
automotive instrument clusters and is shown
in Figure 3. The SA5775 receives a 10-bit
serial word and converts that word to four
voltage outputs that appear at the SINE+,
SINE–, COSINE+, and COSINE– outputs.
The differential voltage at the SINE outputs
are applied to one coil of the meter and the
COSINE outputs are applied to the other coil
of the meter.
The currents through these coils produce a
resultant magnetic force which is the vector
sum of the magnetic forces produced by
each of the two coils. Since the currents
through the coils are bidirectional this
magnetic vector can rotate through a full 360
degrees. The magnetized disc within the air
core meter will follow the rotating vector and
the needle will indicate the vector’s current
position. Since 10 bits are used, there are
1024 discrete words available resulting in an
angular displacement of 0.3516 degrees per
bit. This is small enough to provide an
apparently smooth movement of the needle.
The smoothness of the motion will depend
greatly on the damping factor of the meter
movement.
A simplified block diagram of the SA5775 is
shown in Figure 4. This device consists of a
serial-in/parallel-out shift register, a data
latch, a D/A converter, a multiplexer, and
output buffers.
A logic high must be present on the chip
select (CS) input to clock in the data. Data
appearing on the data input (DI) pin is
clocked into the shift register on the rising
edge of the clock (CLK) input. The data
output (DO) pin is the overflow from the shift
register, allowing the user to daisy chain
multiple SA5775 devices. Note that data is
clocked out of this pin on the falling edge of
the clock. The CS pin is also used to latch
the parallel outputs of the shift register into
the data latch. The outputs of the data latch
feed the inputs to the D/A converter. The D/A
converter outputs are buffered to form the
drive signals for the meter coils.
The D/A converter circuits, multiplexer and
associated output buffers are purposely
designed such that the span of these circuits
do not include the power supply rails. This is
to avoid inaccuracies that would otherwise
occur if the output were to become very close
to either supply rail. With a supply voltage of
14 volts (VIGN), the outputs will span a range
of approximately 1 to 11 volts. The SA5775 is
designed to drive air core meters having a
minimum winding impedance of 180at
–40°C.
The clock high and low time requirements are
175ns minimum and the maximum data rate
is 1.6 megabits per second. At this rate it
would require approximately 6.4ms to ramp
from zero to full scale if all binary codes were
loaded into the SA5775. However, the air
core meter cannot respond to such data
rates. Both inertia of the movement and
damping build into the design of typical air
core meter movements limit their response
speed.
A high on the output enable input pin (OE) is
required to permit the SA5775 to drive the air
core gauge. In Figure , OE is held low while
the microcontroller is being reset to prevent
the gauge from being driven.
P3.4/A4 1
P3.3/A3 2
P3.2/A2/A10 3
P3.1/A1/A9 4
P3.0/A0/A8 5
P0.2/VPP 6
P0.1/SDA/ 7
OE–PGM
P0.0/SCL/ 8
ASEL
RST 9
X2 10
X1 11
VSS 12
CERAMIC
AND
PLASTIC
DUAL
IN-LINE
PACKAGE
AND
SHRINK
SMALL
OUTLINE
PACKAGE
24 VCC
23 P3.5/A5
22 P3.6/A6
21 P3.7/A7
20 P1.7/T0/D7
19 P1.6/INT1/D6
18 P1.5/INT0/D5
17 P1.4/D4
16 P1.3/D3
15 P1.2/D2
14 P1.1/D1
13 P1.0/D0
4 1 26
5 25
PLASTIC
LEADED
CHIP
CARRIER
11 19
12 18
Pin Function
Pin Function
1 P3.4/A4
15 P1.0/D0
2 P3.3/A3
16 P1.1/D1
3 P3.2/A2/A10
17 P1.2/D2
4 P3.1/A1/A9
18 P1.3/D3
5 NC*
19 P1.4/D4
6 P3.0/A0/A8
20 P1.5/INT0/D5
7 P0.2/VPP
21 NC*
8 P0.1/SDA/OE-PGM 22 NC*
9 P0.0//SCLASEL
23 P1.6/INT1/D6
10 NC*
24 P1.7/T0/D7
11 RST
25 P3.7/A7
12 X2
26 P3.6/A6
13 X1
27 P3.5/A5
14 VSS
28 VCC
* DO NOT CONNECT
SU00315
Figure 1. Pin Configuration
January 1992
5-8 Revision date: 1995 Nov 01




Philips

AN426 Datasheet Preview

AN426 Datasheet

Controlling Air Core Meters

No Preview Available !

Philips Semiconductors
www.datasheet4u.com
Controlling air core meters with the 87C751 and SA5775
Application note
AN426
COSP
COSM
SINP
SINM
SA5775
ACMD
P3.5
P3.6
VCC
87C751
P1.0
P1.1
P1.2
P1.3
P3.2
P3.3
P3.4
RST
P3.0
P3.1
January 1992
Figure 2. Interface Between the 87C751 and the Philips SA5775
5-9
SU00373A


Part Number AN426
Description Controlling Air Core Meters
Maker Philips
PDF Download

AN426 Datasheet PDF






Similar Datasheet

1 AN42 CMOS Gate Array
AMI
2 AN4250 Single Low Power Consumption Operational Amplifiers
Panasonic Semiconductor
3 AN4250S Single Low Power Consumption Operational Amplifiers
Panasonic Semiconductor
4 AN426 Controlling Air Core Meters
Philips





Part Number Start With

0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F    G    H    I    J    K    L    M    N    O    P    Q    R    S    T    U    V    W    X    Y    Z



Site map

Webmaste! click here

Contact us

Buy Components

Privacy Policy