ARCHIVED 2005 AN1655 ASB200 - Sensor Development Controller Board

MOTOROLA
Freescale Semiconductor, Inc.
SEMICONDUCTOR APPLICATION NOTE
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
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by AN1655/D
AN1655
ASB200 Ċ Motorola Sensor Development
Controller Board
An MC68HC705JP7 based controller board that is part of a
systems development tool set for pressure sensors is
presented here. When used with a series of companion
plug–in modules, it provides a complete systems solution for
measuring pressure and developing code.
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
Freescale Semiconductor, Inc...
Prepared by: Bill Lucas and Warren Schultz
SENSOR DEVELOPMENT
CONTROLLER DESCRIPTION
Function
The development board shown in Figure 1 is designed to
receive signal inputs from a series of pressure sensor
modules, receive command inputs via a dip switch or a
terminal’s keyboard, process the input signal, and send
results to a terminal or liquid crystal display. Temperature
display is an optional output of the system.
The ASB200 Sensor Development Controller will run in two
configurations. As delivered, it will operate on its own with the
pre–programmed microcontroller supplied with the board. Or,
for code development, it will connect to an M68EM05JP7
emulator via an M68CBL05A cable and M68TA05JP7P28
target head adapter, when the microcontroller is removed. The
emulator board may be run on either an MMDS05 or
MMEVS05 system.
The input connector (P1) connects any one of several
plug–in modules. At the time of this publication the following
modules are supported by the system’s hardware and
software:
• ASB 201: Uncompensated Series Sensor Module
• ASB 202: MPX2000 Compensated Series Sensor
Module
• ASB 205: MPX5000 Integrated Series Sensor Module
• ASB 210: MPX2010 Low Pressure Module
Figure 1. ASB200 — Development Controller Board
REV 1
Motorola Sensor Device Data
 Motorola, Inc. 1998
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Electrical Characteristics
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
The following electrical characteristics apply to operation at 25 degrees Celsius, and unless otherwise specified B+ = 12 volts.
Table 1. ASB200 Electrical Characteristics
Characteristic
Symbol
B+
Power Supply Voltage
— Stand alone
— Connected to ASB201
— Connected to ASB202
— Connected to ASB205
— Connected to ASB210
Quiescent Current
Min Analog Input Voltage
Buffer Gain
— VS1 Input
— VS2 Input
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Max Analog Input Voltage
Resolution
Output Sink Current
Content
The ASB200 controller includes an MC68HC705JP7
microcontroller, liquid crystal display (LCD), RS232
communications interface, EEPROM, a 5 volt regulator, and
an analog input interface. Its contents are described in the
2
Min
Typ
Max
Units
7.5
9.5
11.6
7.5
22
12
12
12
12
24
26
15.8
15.8
26
26
Volts
Volts
Volts
Volts
Volts
ICC
—
25
—
mA
VIN(MIN)
VIN(MAX)
50
—
—
mV
—
—
5.0
Volts
AVS1
AVS2
—
—
1.0
1.0
—
—
—
—
A/DRES
ISINK
10
10.5
—
Bits
—
25
—
mA
following parts list, schematics, and pin by pin circuit
description. Software is programmed into the microcontroller
and is also supplied on an enclosed disk. The disk also
includes PSPICE models for Uncompensated, MPX2000, and
MPX5000 series sensors.
For More Information On This Product,
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Motorola Sensor Device Data
Freescale Semiconductor, Inc.
AN1655
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
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Table 2. Parts List
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
Freescale Semiconductor, Inc...
Designators
Qty
Description
Manufacturer
Part Number
C1
1
.12 µf Capacitor Polypropylene
Digi–Key
P3214
C2,3,9,18,19
5
22 pf Capacitor Cer
Digi–Key
P4841
C4,5,6,7,11,16
6
1 uF Electrolytic 50V Cap
Digi–Key
P5268
C8
1
.01 uF Cap
Digi–Key
P4904
C10
1
470 pf Capacitor
Digi–Key
P4808
C12,13,14,15,17,20
6
.1UF CAP
Digi–Key
P4910
D1
1
General Purpose Diode
Motorola
1N4002
D2
1
Red LED
Quality Tech
HLMP–4700
D3,D4,D5,D6
4
1N914
—
1N914
LCD1
1
4 DIGIT LCD
AND
FE0202W–DU
P1 SENSOR INTERFACE
1
DB–9 Connector (Male)
AMP
#177597–3
P2 TERMINAL INTERFACE
1
DB–9 Connector (Female)
Mouser
#152–3409
RP1
1
10K 10 PIN SIP Resistor
Digi–Key
770–101–R10K–ND
R1
1
47K Ohm Resistor
Yaego
47K CR–1/4W–B 5%
R2,R5,R12,R13
5
750 Ohm Resistor
Yaego
750 CR–1/4W–B 5%
R3,R4,R6,R7,R9,R11,R14
1
10K Ohm Resistor
Yaego
10K CR–1/4W–B 5%
R8
1
470K Ohm Resistor
Yaego
470K CR–1/4W–B 5%
R10
1
470 Ohm Resistor
Yaego
470 CR–1/4W–B 5%
SW1
1
8 POS DIP SWITCH
Digi–Key
CAN3007
SW2,3
1
SPST Pushbutton Switch
NKK
AB15AP–FA
TP1 Vout
1
Test Point Yellow
Components Corp.
TP–104–01–04
TP2 Vtemp
1
Test Point Yellow
Components Corp.
TP–104–01–04
TP3 KGND, TP4 GND
2
Test Point Black
Components Corp.
TP–104–01–00
JT1
1
5 Screw Terminal Connector
Phoenix Contact
MKDSN 1,5/5–5,08
JT2
1
2 Screw Terminal Connector
Phoenix Contact
MKDSN 1,5/2–5,08
U1
1
Microprocessor MC68HC705JP7
Motorola
MC68HC705JP7
U1X
1
28 pin Socket
Digi–Key
AE7228–ND
U2
1
256 Bit Serial EEPROM
National
NM93C06N 8 PIN DIP
U3
1
RS–232 Driver/Receiver
Motorola
MC145407P
U4
1
Dual Op–Amp
Motorola
MC33502P
U5
1
Quad Bus Driver
Motorola
MC74HC125P
U6
1
32 Segment LCD Driver
Motorola
MC145453P
U7
1
SPI/Microware–Compatible UART
Maxuim
MAX3100CPD 14 PIN DIP
VR1
1
Voltage Regulator
Motorola
MC7805ACT
Y1
1
4.00 MHz Crystal
Digi–Key /CTS
X405–ND
Y2
1
3.6864 MHz Crystal
Digi–Key /CTS
X402–ND
—
2
Insulator for Y1 and Y2
Bivar
C1–192–028
—
1
4–40 x 1/4″ Screw for VR1
—
—
—
1
4–40 Nuts for VR1
—
—
—
6
Self stick rubber feet
Fastex
5033–01–00–5001
ASB200
1
Bare PCB
—
—
ASB200
—
—
—
—
Rev. 1.0
Note 1: All resistors are 1/4 W with a tolerance of 5% unless otherwise noted.
Motorola Sensor Device Data
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RP1
10 k X 9
U1
1 2 3 4 5 6 7 8 9 10
+5
1
2
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SW1
1
16
3
2
15
4
3
14
5
4
13
6
5
12
7
6
11
8
7
10
9
8
9
SW1–7
10
SW1–8
11
DIP SWITCH 8
1 UP = AUTO ZERO
2 UP = FULL SCALE CAL
3, 4, 5, 6 = SENSOR TYPE
7, 8 = ENGINEERING UNITS
12
C21
22 pF
13
14
C1
28
PB1/AN1
PB0/AN0
PB2/AN2
VDD
PB3/AN3/TCAP
VSS
PB4/AN3/TCMP
OSC1
0.12
27
+5
26
C2
25
24
PB5/SD0
Y1
23
+5
C3
22 pF
PC3
22
PC5
21
PC6
PC1
20
PC7
PC0
SW1–7
STAT_1
SW1–8
STAT_0
19
*RESET
18
IRQ/VPP
17
PA5
PA0
16
PA4
PA1
15
PA3
Vout
Vtemp
PC2
PB7/SCK
4.0 mHz
OSC2
PC4
PB6/SDI
22 pF
PA2
*RESET_IN
JP7_IRQ
CNTL_OUT
LCD_CLOCK
*CALIBRATE
68HC705JP7
*SCI_SEL
U2
+5
8
7
6
5
VCC
CS
*STR
SK
*RCL
DI
VSS
DO
NM93C06M8
1
LCD_DATA
2
SPI_SCK
3
SPI_SDO
4
SPI_SDI
R1
47 k
Figure 2a. Schematic
4
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23
DB1
DB2
DB3
DB4
DB5
DB6
DB7
DB8
DB9
DB10
DB11
DB12
DB13
DB14
DB15
DB16
DB17
DB18
DB19
DB20
DB21
DB22
DB23
DB24
DB25
DB26
DB27
DB28
DB29
DB30
DB31
DB32
DB33
BPin
BPout
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
38
2
36
37
5
6
7
34
35
8
31
32
9
10
11
29
30
12
26
27
13
14
15
24
25
16
22
23
17
18
19
20
21
1
BACKPLANE
LCD1
VDD
20
OSCin
VSS
CLOCK
DATA
19
1
21
22
R8
C10
470 k
470 pF
LCD_DATA
+5
LCD_CLOCK
+5
R9
10 k
SW2
3
1
2
R10
470
*CALIBRATE
SPST PUSHBUTTON
D2
LED
+5
1N4002
D1
1
1
B+
GND
+
C11
1.0 mF
VIN
2
VOUT
GND
2
R11
10 k
SW3
3
1
2
VR1
MC7805ACT
B+
JT2
U6
MC145453P
*RESET_IN
SPST PUSHBUTTON
3
+5
+
C12
0.1
C13
0.1
C14
0.1
C15
0.1
C16
1.0 mF
C20
0.1
KGND
TP3
C17
0.1
TP4
GND
Figure 2b. Schematic
Motorola Sensor Device Data
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1
SPI_SDO
U7
Din
14
SPI_SDI
13
Dout
TX
SCLK
RX
3
SPI_SCK
RTS
*IRQ
CTS
5
JP7_IRQ
R14
X1
GND
X2
7
+5
10 k
8
+5
Y2
MAX3100
RX3
DI2
TX2
DO2
RX2
DI1
TX1
DO1
RX1
VDD
VSS
C1–
C2–
VCC
GND
C1+
C2+
16
C4
1.0 mF
+
2
1
C6 +
1.0 mF
+5
5
9
9
8
4
7
8
6
3
4
18
19
20
P2
10
5
17
C18
22 pF
3.6864 mHz
C19
22 pF
C5
1.0 mF
2 1
+
7
2
6
3
2
1
+
1
C7
1.0 mF
RS–232
TERMINAL
INTERFACE
MC145407P
+5
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DO3
15
9
*SHDN
TX3
14
10
6
+5
DI3
13
11
*CS
U3
12
12
4
*SCI_SEL
+5
–VCC
2
11
TP2
U4A
1
Vtemp
3
+
2
–
P1
R2
+5
C8
0.01
D4
1N914
MC33502
750
3
STAT_1
2
1
+5
B+
U5A
MC74HC125
R13
750
+5
D3
1N914
R3
10 k
5
+5
9
B+
4
R4
8
10 k
3
VS2
STAT_1
VS1
7
+5
TP1
7
Vout
U4B
5
+
6
–
C9
22 pF
D6
1N914
MC33502
STAT_0
2
D5
1N914
KGND
6
R5
CNTL
1
750
GND
+5
R12
U5B
MC74HC125
6
+5
U5C
MC74HC125
750
5
STAT_0
4
8
9
10
CNTL_OUT
NOTE:
U4 pin 4 connects to GND
U4 pin 8 connects to +5
U5 pin 7 connects to GND
U5 pin 14 connects to +5
SENSOR
INTERFACE
R6
10 k
VS2
R7
10 k
VS1
KGND
U5D
MC74HC125
12
11
13
GND
JT1
SENSOR
INTERFACE
Figure 2c. Schematic
6
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Pin by Pin Description
Screw Connector JT1
External inputs and outputs are grouped into two DB–9
connectors and two screw terminals. Connector P1 is the
interface connection to ASB201, ASB202, ASB205, and
ASB210 sensor plug–in modules. Screw terminal JT1,
auxiliary sensor interface, is intended for stand alone
operation with user supplied code. Screw terminal JT2 is the
DC power input connector. Connector P2 is an RS–232
interface connection that allows optional 9600 baud
communications with a terminal.
Connections for +5, VS1, VS2, KGND, & GND are wired in
parallel with DB–9 connector P1.
Screw Connector JT2
P2–3:
Pin 3 is routed to the RS–232 signal input.
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B+ :
B+ is the power supply input. Power supply voltage varies with
plug–in module, per Table 1. +12 VDC is the nominal input
voltage, except for use with ASB210 plug–in modules, where
it increases to +24 VDC.
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AN1655
GND:
The GND terminal on this connector is used as the return for
power supply B+.
DB–9 Male Sensor Module Interface Connector P1
P2–1:
Pin 1 is connected to an RS–232 Handshake line, that is also
connected to pins P2–4 and P2–6.
P2–2:
Pin 2 is routed to the RS–232 signal output.
P2–4:
Pin 4 is connected to an RS–232 Handshake line, that is also
connected to P2–1 and P2–6.
P2–5:
Pin 5 connects to ground.
P2–6:
Pin 6 is connected to an RS–232 Handshake line that is also
connected to P2–4 and P2–1.
P2–7:
Pin 7 is connected to an RS–232 Handshake line, that is also
connected to P2–8.
P1–1:
Pin 1 is connected to Logic ground.
P1–2:
A connection to Analog Ground is made on Pin 2.
P1–3:
Analog input signal, VS1, is connected to pin 3. When
connected to an ASB201, ASB202, ASB205, or ASB210
plug–in module, VS1 is the analog pressure signal. This signal
is buffered and connected to A/D mux. AN2.
P1–4:
Analog input signal, VS2, is connected to pin 4. When
connected to an ASB201, ASB202, ASB205, or ASB210
plug–in module, VS2 is the analog temperature signal. This
signal is buffered and connected to A/D mux. AN1.
P1–5:
Regulated +5 VDC from linear regulator VR1 is supplied on
pin 5.
P1–6:
A control signal, CNTL, is supplied on pin 6. It is a logic level
buffered output from the microprocessor’s PORT A, bit 0.
P1–7:
An identification bit, STAT_0, is a logic input that is pulled up,
buffered, and routed to the microprocessor’s PORT C, bit 2.
On plug–in modules ASB201 and ASB202 this bit is grounded.
On plug–in modules ASB205 and 210 it is open, and pulled up
to a logic 1.
P1–8:
An identification bit, STAT_1, is a logic input that is pulled up,
buffered, and routed to the microprocessor’s PORT C, bit 3.
On plug–in modules ASB201 and ASB205 this bit is grounded.
On plug–in modules ASB202 and 210 it is open, and pulled up
to a logic 1.
P1–9:
B+ from screw terminal JT2 is connected to pin 9.
Motorola Sensor Device Data
DB–9 Female RS–232 Connector P2
P2–8:
Pin 8 is connected to an RS–232 Handshake, that is also line
connected to P2–7.
P2–9:
Not connected.
Test Points
Test points TP1 and TP2 provide access to buffered inputs
VS1 and VS2, connected to A/D inputs AN2 and AN1
respectively. When connected to an ASB201, ASB202,
ASB205, or ASB210 plug–in module, VS1 is the analog
pressure signal, and VS2 is the analog temperature signal.
Switches
SW1:
SW1 is an 8 position dip switch that sets mode of operation.
It controls autozero, full scale or zero calibration, inputs sensor
type, selects Engineering units, and also has a position for
restoring factory calibration. The operation section of this
document explains switch settings in detail.
SW2:
SW2 is used for calibration and for restoring factory EEPROM
calibration values.
SW3:
SW3 provides a processor RESET function to restart the
program residing in the 68HC705JP7 microprocessor.
OPERATION
An example, shown in Figure 3, illustrates connections to an
ASB202 plug–in module. This arrangement can be run stand
alone, or the ASB200 can be connected to an MMDS05 or
MMEVS05 emulator system for code development. The two
boards are designed such that their P1 connectors mate
directly. A short straight–through cable with male and female
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is turned on, “dLy” will appear on the display for a short time
while autozeroing is performed. Once a zero appears, the
system is ready for operation. The system has two modes of
operation. They are non–terminal and terminal modes.
Non–terminal mode is discussed first.
DB–9 connectors on the ends may be used between the
controller and the plug–in module. Once the two boards are
connected together, power supply voltage B+ should be set to
the range referenced in Table 1 for the plug–in module that is
being used. With switch SW1 set up as shipped, when power
+12 VDC
POWER
SUPPLY
GND
LCD
OPTIONAL
TERMINAL
SETTINGS:
9600 BAUD
8 DATA BITS
NO PARITY
1 STOP BIT
FULL DUPLEX
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B+
B+
JT2
GND
KGND
CNTL
VS1
+5
B+
Freescale Semiconductor, Inc...
GND
RS–232
INTERFACE
RANGE
MOTOROLA
ASB202
SENSOR
INTERFACE
P2
P1
MPX2000 SERIES SENSOR MODULE
PRESSURE
SOURCE
+5
VS2
VS1
MICROCONTROLLER
KGND
GND
SW1
JT1
DIP
SWITCH
ASB200
CALIBRATE
RESET
MOTOROLA SENSOR DEVELOPMENT CONTROLLER
Figure 3. Connections
switch is pushed. Positions 3 through 6 select full scale
pressure, select temperature, and contain a switch position for
restoring factory calibration values. Positions 7 and 8 on switch
SW1 set display units. The choices are inches of water column,
kilo Pascals (kPa), and pounds per square inch. As shipped,
switch positions are set for autozero, 10 kPa sensors, and kPa.
It is not necessary to set switch positions for plug–in module
type. The plug–in module is sensed from pins 7 & 8 on
connector P1. Table 3 identifies switch SW1 settings.
Non–Terminal Mode
The software looks for several pieces of information. In
non–terminal mode, that information is picked–up from the
dip–switch SW1. Figure 4 takes a close up look at switch SW1.
Position 1 controls the autozero function. In the up position
autozero is performed at reset, in the down position autozero
is not performed. Switch position two controls calibration. In the
up position, full scale is calibrated when the calibrate switch is
pushed; and when down, zero is calibrated when the calibrate
CALIBRATE FULL SCALE
AUTOZERO “ON”
UNITS
UP
DOWN
1
2
3
4
5
6
7
AUTOZERO “OFF”
CALIBRATE ZERO
Figure 4. Switch SW1
8
8
PRESSURE RANGE
TEMPERATURE
RESTORE FACTORY
CALIBRATION
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AN1655
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Table 3A. DIP Switch SW1 Positions 1 & 2
SW1–1
SW1–2
Function
DOWN
—
AUTOZERO “OFF’’
UP
—
AUTOZERO “ON’’
—
DOWN
CALIBRATE ZERO
—
UP
CALIBRATE FULL SCALE
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Table 3B. DIP Switch SW1 Positions 3–6
SW1–3
SW1–4
SW1–5
SW1–6
DOWN
DOWN
DOWN
DOWN
Sensor
DOWN
DOWN
DOWN
UP
10 kPa: MPX10, MPX2010, MPX5010
DOWN
DOWN
UP
DOWN
50 kPa: MPX50, MPX2050, MPX5050
DOWN
DOWN
UP
UP
DOWN
UP
DOWN
DOWN
DOWN
UP
DOWN
UP
700 kPa: MPX5700
DOWN
UP
UP
DOWN
1000 kPa: MPX5999
DOWN
UP
UP
UP
UP
UP
UP
DOWN
UP
UP
UP
UP
6 kPa: MPX5006
100 kPa: MPX100, MPX2100, MPX5100
200 kPa: MPX200, MPX2200
2.5 kPa: ASB210 with MPX2010 Sensor
Temperature
Restore Factory Calibration
ÁÁÁÁÁÁÁÁÁÁ
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Table 3C. DIP Switch SW1 Positions 7 & 8
SW1–7
SW1–8
Display Units
DOWN
DOWN
DOWN
UP
’’H2O
kPa
UP
DOWN
PSI
Calibration
Calibration is a simple process, once dip–switch SW1 is set
up for the correct sensor and engineering units. To calibrate
zero pressure, set dip–switch SW1 position 2 to the down
position, apply zero pressure to the pressure sensor, and
press and release the “CALIBRATE” push–button. The
display will output “dLy” while the “CALIBRATE” switch is
depressed. (Depressing the “CALIBRATE” switch more than
once is OK). The EEPROM location, for that sensor family,
now has a measured offset calibration value specific to the
sensor and sensor module that is being used. When using
MPX2000 or MPX5000 series sensors this procedure or
autozero is all that is needed for a good measurement.
For the most accurate measurement, full scale can also be
calibrated. To calibrate full scale pressure first calibrate zero
pressure, then set dip–switch SW1 position 2 to the up
position, apply full scale pressure to the pressure sensor, and
press and release the “CALIBRATE” push–button. The
display will output “dLy” while the “CALIBRATE” switch is
depressed. (Again, depressing the “CALIBRATE” switch more
than once is OK). The EEPROM location, for that sensor
family, now has a measured full scale calibration value specific
to the sensor and sensor module that is being used. Full scale
is the full scale rating of the sensor type that has been
Motorola Sensor Device Data
selected, with the exception of ASB210 plug–in modules. For
the ASB210, full scale is the full scale pressure rating of the
module, which is 10 inches of water. Since calibration values
are stored in EEPROM they are retained when power is
removed. NOTE, THAT FOR BEST RESULTS IT IS
NECESSARY TO CALIBRATE ZERO PRESSURE BEFORE
CALIBRATING FULL SCALE. That’s all there is to it,
calibration is complete at this point.
Autozero
Autozero is controlled by dip–switch SW1 position 1. That
switch is read at RESET/POWER–UP time. In the up position
autozero is performed at power up, in the down position it is
not. With SW1 position 1 up at power up, the software will read
the sensors output and store its analog value in the EEPROM.
As long as SW1 position 1 is in the up position, that
“auto–zero” value will be used as the sensor’s offset in lieu of
any previously stored calibration values. When SW1 position
1 is placed in the down position, the value from the previously
described calibration procedure will be used. To force a new
“auto–zero” value into EEPROM, set SW1 position 1 up, and
depress the “RESET” push–button, or power the system down
and back up. A new “auto–zero” value will be written to the
EEPROM. You will notice a delay in system start–up when the
SW1–1 (auto–zero switch) is in the up position. The display
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will read “dLy” during the “auto–zero” sequence. If a terminal
is connected to the system, it will output “Waiting for AUTO
ZERO to complete”, followed by “DONE”. The display will then
begin to function, based on the configuration of SW1.
Temperature Display
To display temperature, set dip switch SW1 positions 3
through 5 up and position 6 down. With this setting, analog
voltage VS2 is used as the input, and degrees Celsius will be
displayed. Table 4 contains input voltage, VS2, versus
temperature in five degree Celsius increments from 0 to 75
degrees C. The software performs a segmented straight line
interpolation of these values. The thermister used in plug–in
modules ASB201, ASB202, ASB205, & ASB210 is a
Keystone Thermometrics part number MS97 (also available
through Digi–Key as part number KC003T).
Temperature °C
RT Ohms
VS2 Volts
Temperature °C
RT Ohms
VS2 Volts
0
32773
1.17
40
5323
3.26
5
25456
1.41
45
4365
3.48
10
19932
1.67
50
3599
3.68
15
15725
1.94
55
2983
3.85
20
12497
2.22
60
2486
4.00
25
10000
2.50
65
2082
4.14
30
8055
2.77
70
1753
4.25
35
6528
3.03
75
1482
4.35
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Table 4. VS2 vs Temperature
Restoring Factory Calibration Constants/Troubleshooting
To restore default factory calibration constants, set dip
switches SW1–1 and SW1–2 in the down position, and
SW1–3 through SW1–6 in the up position. Press and release
the “CALIBRATE” push–button, located in the lower right of
the ASB200 PC board. The display will output “dLy” while the
“CALIBRATE” switch is depressed. (Depressing the
“CALIBRATE” switch more than once is OK.) The EEPROM
now has factory calibration constants transferred to it. Note
that this is the first thing to do when readings don’t seem
to make sense. Other items to check include power supply
voltage B+, and display units setting. B+ should be in spec, per
Table 1, for the plug–in module that is being used. SW1–7 and
SW1–8 should be set for the units that you are expecting per
Table 3C.
Terminal Mode
The ASB200 serial port P2, labeled RS–232 TERMINAL
INTERFACE is always enabled and monitored for activity.
Terminal emulation software running on a Personal Computer
(PC), will communicate with this port. Settings are listed in
Table 5.
Table 5. Terminal Settings
Baud
Data Bits
Parity
Stop Bits
Duplex
9600
8
NO
1
FULL
When commanded to do so, via the terminal, the ASB200
can be switched to TERMINAL MODE, where most control of
the system is performed by keyboard menu entries. When
10
TERMINAL MODE is activated, the system continues to use
dip switch SW1 position 1 for auto–zero and SW1 positions 3
through 6 for sensor type.
Connecting the ASB200 to an IBM Compatible PC
1. With power removed from the ASB200, and the PC
powered off, connect a 9 conductor straight–through
cable from the ASB200 connector P2, labeled “RS–232
TERMINAL INTERFACE” to the COM1 or COM2 serial
port on the PC.
2. Restore power to the PC.
3. If you are using DOS based communications software
such Procomm, set the COM port to COM1 or COM2
depending on which PC port you have cabled to
ASB200 connector P2. Set the BAUD rate to 9600, the
number of data bits to 8, the number of stop bits to 1 and
the parity to NONE. Set the communications mode to
full duplex.
4. Restore power to the ASB200 board. The system will
start in the non–terminal mode. To activate terminal
mode, depress any key on the terminal keyboard. (SW1
must be set per Table 3 when entering terminal mode or
the display will display “Err”. The error will occur if SW1
was set to display temperature or in the restore factory
calibration mode when the system was put in terminal
mode). A “Main Menu” will appear on the terminal’s
display. The menu is shown in Figure 5. Menu choices
are driven by a single keystroke. Depressing the “Enter”
key on the keyboard is unnecessary.
Follow the instructions on the PC’s display while in
terminal mode.
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Terminal Mode Main Menu
The main menu as shown in Figure 5 allows the following
command options:
1. Display the pressure applied to the pressure sensor.
terminal mode. The values displayed are in percent of
full scale times 10, i.e., if the one of the values in the
EEPROM reads 123, that value indicates an A/D value
of 12.3% of Vref or 12.3% of 5 volts.
2. Display the temperature of the thermister, located on the
pressure sensor plug–in module.
6. The choices of engineering display units for the
pressure sensor are pounds per square inch, kilo
Pascal’s and inches of water column.
3. Calibrate the system for the sensor’s zero pressure
offset calibration.
7. You can exit terminal mode by depressing the numeric
7 key on the terminal’s keyboard.
4. Calibrate the system for the sensor’s full scale input
calibration.
5. Dump the contents of EEPROM. The EEPROM
contains the calibration results of menu items 3 and 4,
auto–zero values, as well as the display units used in
8. Factory calculated calibration constants can be
reloaded into EEPROM by depressing the 0 numeric
key. These constants are approximations of calibration
values for the various pressure sensors supported by
the system. These constants will overlay any user
calibrations that have previously been performed.
Terminal – ASB200.trm
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AN1655
Main Menu:
Press 1 to display PRESSURE.
Press 2 to display TEMPERATURE.
Press 3 for ZERO PRESSURE calibration.
Press 4 for FULL SCALE calibration.
Press 5 to dump EEPROM contents.
Press 6 to set pressure DISPLAY ENGINEERING UNITS.
Press 7 to exit TERMINAL MODE.
Press 0 to RESTORE factory EEPROM calibration default values.
Your choice ? _
Figure 5. ASB200 Main Menu
DESIGN CONSIDERATIONS
The MC68HC705JP7 microcontroller was chosen for a
pressure measurement system reference design because of
its 10+ bit A/D converter resolution and its low cost. From a
hardware point of view, this microcontroller facilitates a
relatively simple design.
Given the ASB200’s intended use as a development tool, all
inputs and outputs, both analog and digital, are buffered.
Analog inputs are buffered with MC33502 operational
amplifiers configured for unity gain. These buffers provide a
high input impedance, and also present a low source
impedance to the JP7’s A/D converter inputs. Low impedance
at the A/D converter inputs is an important consideration,
since the A/D converter’s input impedance is nominally 120K
ohms, as configured by the ASB200’s software. Digital
buffering, to and from connector P1, is performed with an
MC74HC125 bus driver IC.
The LCD driver, MC145453, is an SIOP compatible
peripheral, however, it has no chip select. Due to the lack of
Motorola Sensor Device Data
a chip select on the LCD driver, a software emulated SIOP was
constructed using two I/O lines from the microcontroller.
An SIOP/SPI compatible UART, MAX3100, was added for
communications to an optional terminal. A UART could have
been software generated by using two I/O lines from the
microcontroller. However, due to the amount of interrupt
driven functions in the A/D software driver, it made sense to
add a true UART to the system.
A small EEPROM is included in the design as a convenient
way to store calibration information for the system.
Last but not least, board layout is an important design
consideration. In particular, how grounds are tied together
influences noise immunity. In order to maximize noise
immunity, two grounds are used. Digital ground (GND) is
common to the power supply return and serves as a general
purpose ground. An analog ground (KGND) ties the analog
input return, op amp U1’s signal grounds, and C1’s ground
together before connecting with digital ground at only one
point. KGND also runs as a separate trace to P1–2 and the
screw terminal labeled KGND on screw connector JT1.
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Basic operating software is programmed into the
microcontroller supplied with the ASB200 printed circuit
board. The software, provides for calibration, reads pressure,
reads temperature, and displays the results on a Liquid
Crystal Display (LCD). It also provides an output signal,
labeled CNTL, that lights the “RANGE” light on ASB201,
ASB202, and ASB205 plug–in modules when full scale
pressure is exceeded. When the presence of an ASB210 low
pressure module is detected with logic highs at pins 7 and 8
of DB–9 connector P1, this signal is used to control power to
the sensor.
Three source modules, a link command file (ASB200.lnk),
an I/O file (IO.h), a read me file, and a batch file (ASB200.bat)
for compiling and linking the code are contained on a 3.5″
floppy diskette that is included with the ASB200 board. They
are in a folder labeled, JP7code. The three source files are
asb200.c, crt.s, and vector.c. File asb200.c is a single ‘C’
source file containing the code that operates the system. File
crt.s is an assembly language file containing startup code
required by the system, and vector.c is a ‘C’ source file
containing reset and interrupt vector information. These
modules are compiled by a compiler from:
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SOFTWARE FUNCTIONAL OVERVIEW
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init_io
init_io sets–up the processors I/O ports, switches the oscillator
to the external crystal, sets–up the processor’s real time
interrupt, powers–up the A/D comparators, sets–up the input
capture edge, initializes the first A/D mux address, configures
the UART driver, configures the LCD driver, and performs an
auto zero if requested by dip switch SW1 position 1.
wr_write_siop
wr_write_siop writes a byte to the Simple Synchronous I/O
Interface (SIOP) and returns the input data from that port.
write_siop
write_siop writes a byte to the Simple Synchronous I/O
Interface (SIOP).
cvt_bin_dec
cvt_bin_dec formats and writes data to the liquid crystal
display.
write_lcd
write_lcd writes 8 bits of clock and data to the MC145453 LCD
driver IC.
read_temperature
read_temperature computes the temperature based upon the
value of analog signal VS2 connected to A/D converter input
AN1.
display
display determines which output device receives computed
A/D results. The choice is the LCD, UART or both.
Some source code changes will likely be necessary for
compilation with compilers from other vendors. To compile the
files, consult the readme.doc file on the diskette. A brief
description of each module follows:
crt.s
crt.s is an assembly startup module that zeros RAM, places an
op–code in RAM that is used by the C’ compiler’s runtime
support, and calls the main routine.
ee_wren
ee_wren sends a code enabling data writes to EEPROM.
ee_write
ee_write writes 16 bits of data to the EEPROM at a specified
address.
ee_read
ee_read reads a 16 bit word from a specified address in the
EEPROM.
vector.c
vector.c is a C’ source file, containing reset and interrupt
vectors.
config_uart
config_uart configures the UART for 9600 baud, no party, and
2 stop bits. The 2 stop bits are for slow terminals.
asb200.c
The following functions are contained in file asb200.c:
read_uart
read_uart reads a character from the terminal. If no character
is available, 0 is returned.
p_timer
p_timer is the interrupt service routine used by the input
capture hardware. It serves as an A/D completion interrupt for
the A/D subsystem. The ramp time for the integrating
capacitor is computed here and saved for use by the interrupt
routine, c_timer.
c_timer
c_timer is the CPU core’s real time interrupt service routine.
This routine sets–up the next analog multiplexer address,
computes the unknown analog inputs on AN1 and AN2 based
on the internal Vdd reference, initiates the next A/D
conversion, and performs an infinite impulse filter on
conversion results. It also handles analog time–out, if one
occurs.
12
write_uart
write_uart writes a character to the terminal.
out_2uart
out_2uart formats and writes integer data to the terminal.
read_pressure
read_pressure computes pressure from the analog voltage,
VS1, connected to A/D converter input AN2. Scaling, based
on display units and the sensor type, is computed here as well.
dump_eeprom
dump_eeprom outputs the contents of the EEPROM.
Calibration contents for the various sensors are displayed as
percent of full A/D scale times 10, i.e., the output 400 equals
40% full scale. All values are ratiometric to the +5 volts that is
applied to the microcontroller.
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print_text
print_text outputs a text string to the terminal until a null (0)
character is detected in the string.
restore_eeprom
restore_eeprom transfers factory calibration constants from
the program into the EEPROM. These factory constants are
approximations of the analog output from the various sensor
boards.
menu
menu reads the UART and parses terminal commands.
display_pressure
display_pressure directs pressure values to the terminal,
LCD, or both, based on terminal or non–terminal mode.
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display_temperature
display_temperature directs temperature values to the
terminal, LCD, or both, based on terminal or non–terminal
mode.
get_sensor_type
get_sensor_type parses the dip switch, SW1 positions 3
through 6, and returns a sensor type code.
get_eeprom_cal_address
get_eeprom_cal_address retrieves calibration values for the
sensor type picked–up by get_sensor_type and the “board
ID”.
calibrate
calibrate saves the empirical value of the analog voltage from
the pressure sensor to the address appropriate for that sensor
and board type in EEPROM. This function is used in the
non–terminal mode. The calculation for the address of the
offset or full scale of the sensor is picked–up from dip switch
SW1 position 2.
zero_cal
zero_cal saves the empirical value of the analog offset voltage
to the address appropriate for that sensor and board type in
EEPROM. This function is used in terminal mode.
full_scale_cal
full_scale_cal saves the empirical value of the full scale
analog voltage to the address appropriate for that sensor and
Motorola Sensor Device Data
AN1655
board type in EEPROM. This function is used in the terminal
mode.
check_valid_config
check_valid_config uses the “board ID” and dip switch SW1
positions 3 through 6 to determine the validity of the
combination. In other words, it looks for invalid sensor type
and “board ID” combinations. If an error is detected, the LCD
will display “Err” until the error is corrected.
write_lcd_text
write_lcd_text writes a limited text string to the LCD. The string
is blank the LCD, “Err” , or “dLy”.
main
main checks for a valid sensor type/”board ID” combination
and outputs pressure or temperature to the LCD in
non–terminal mode. In terminal mode, main outputs the menu
message to the terminal, and passes control to the menu
routine.
PSPICE Models
In addition to HC05 code, PSPICE models that describe
Uncompensated, MPX2000, and MPX5000 pressure sensors
are included in a folder labeled MODELS. These models use
compound temperature coefficients to describe DC behavior
over a 40 to +125 degree Celsius temperature range. Due
to extensive use of PSPICE’s .PARAMETER function, these
models are specific to PSPICE. In addition to the sensors, the
instrumentation amplifiers used in ASB201, ASB202, and
ASB210 plug–in models are also modeled.
*
CONCLUSION
The ASB200 Sensor Development Controller is part of a
systems development tool set for pressure sensors. It
provides an HC05 based platform for reading pressure and
developing code. Pressure signals are received from
ASB201, ASB202, ASB205, and ASB210 plug–in modules.
Together with MMDS & MMEVS software development tools,
these products provide a comprehensive tool set that
facilitates code development for pressure sensor systems
without the necessity for building hardware.
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AN1655
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NOTES
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AN1655
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NOTES
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AN1655
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