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Application Note
V850 Series
Dual Slope A/D Conversion
32-bit Single-Chip Microcontrollers
Document No. U17227EE1V0AN00
Date Published June 2004
NEC Corporation 2004
Printed in Germany
NOTES FOR CMOS DEVICES
1
PRECAUTION AGAINST ESD FOR SEMICONDUCTORS
Note:
Strong electric field, when exposed to a MOS device, can cause destruction of the gate oxide and
ultimately degrade the device operation. Steps must be taken to stop generation of static electricity
as much as possible, and quickly dissipate it once, when it has occurred. Environmental control
must be adequate. When it is dry, humidifier should be used. It is recommended to avoid using
insulators that easily build static electricity. Semiconductor devices must be stored and transported
in an anti-static container, static shielding bag or conductive material. All test and measurement
tools including work bench and floor should be grounded. The operator should be grounded using
wrist strap. Semiconductor devices must not be touched with bare hands. Similar precautions need
to be taken for PW boards with semiconductor devices on it.
2
HANDLING OF UNUSED INPUT PINS FOR CMOS
Note:
No connection for CMOS device inputs can be cause of malfunction. If no connection is provided
to the input pins, it is possible that an internal input level may be generated due to noise, etc., hence
causing malfunction. CMOS devices behave differently than Bipolar or NMOS devices. Input levels
of CMOS devices must be fixed high or low by using a pull-up or pull-down circuitry. Each unused
pin should be connected to V DD or GND with a resistor, if it is considered to have a possibility of
being an output pin. All handling related to the unused pins must be judged device by device and
related specifications governing the devices.
3
STATUS BEFORE INITIALIZATION OF MOS DEVICES
Note:
Power-on does not necessarily define initial status of MOS device. Production process of MOS
does not define the initial operation status of the device. Immediately after the power source is
turned ON, the devices with reset function have not yet been initialized. Hence, power-on does
not guarantee out-pin levels, I/O settings or contents of registers. Device is not initialized until the
reset signal is received. Reset operation must be executed immediately after power-on for devices
having reset function.
2
Application Note U17227EE1V0AN00
•
The information in this document is current as of 28.06, 2004. The information is subject to change
without notice. For actual design-in, refer to the latest publications of NEC Electronics data sheets or
data books, etc., for the most up-to-date specifications of NEC Electronics products. Not all products
and/or types are available in every country. Please check with an NEC sales representative for
availability and additional information.
•
No part of this document may be copied or reproduced in any form or by any means without prior
written consent of NEC Electronics. NEC Electronics assumes no responsibility for any errors that
may appear in this document.
•
NEC Electronics does not assume any liability for infringement of patents, copyrights or other
intellectual property rights of third parties by or arising from the use of NEC Electronics products
listed in this document or any other liability arising from the use of such NEC Electronics products.
No license, express, implied or otherwise, is granted under any patents, copyrights or other intellectual
property rights of NEC Electronics or others.
•
Descriptions of circuits, software and other related information in this document are provided for
illustrative purposes in semiconductor product operation and application examples. The incorporation
of these circuits, software and information in the design of customer's equipment shall be done
under the full responsibility of customer. NEC Electronics no responsibility for any losses incurred by
customers or third parties arising from the use of these circuits, software and information.
•
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"Special":
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"Specific":
Aircraft, aerospace equipment, submersible repeaters, nuclear reactor control systems,
life support systems and medical equipment for life support, etc.
The quality grade of NEC Electronics products is “Standard” unless otherwise expressly specified in
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Notes:
1.
" NEC Electronics" as used in this statement means NEC Electronics Corporation and
also includes its majority-owned subsidiaries.
2.
" NEC Electronics products" means any product developed or manufactured by or for
NEC Electronics (as defined above).
M8E 02.10
Application Note U17227EE1V0AN00
3
Regional Information
Some information contained in this document may vary from country to country. Before using any NEC
product in your application, please contact the NEC office in your country to obtain a list of authorized
representatives and distributors. They will verify:
•
Device availability
•
Ordering information
•
Product release schedule
•
Availability of related technical literature
•
Development environment specifications (for example, specifications for third-party tools and
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•
Network requirements
In addition, trademarks, registered trademarks, export restrictions, and other legal issues may also vary
from country to country.
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Tel: 408-588-6000
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4
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Application Note U17227EE1V0AN00
Table of Contents
Chapter 1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 2
Description of A/D Conversion Using the Dual Slope Method. . . . . . . . . . . 8
Chapter 3
Derivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Chapter 4
Circuit Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chapter 5
Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1
Calculation of Charging Time and Timer Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.1
Charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.2
Timer setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter 6
6.1
6.2
6.3
Chapter 7
7.1
7.2
7.3
Chapter 8
Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Software Flowcharts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Main Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Measurement Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Application Note U17227EE1V0AN00
5
List of Figures
Figure 4-1:
Figure 7-1:
Figure 7-2:
Figure 7-3:
6
Circuit Diagram............................................................................................................ 10
Main Flow .................................................................................................................... 14
Measurement Flow ...................................................................................................... 15
Data Transmission Flow .............................................................................................. 16
Application Note U17227EE1V0AN00
Chapter 1 Introduction
This application note is written to describe an AD conversion procedure using the V850ES / Fx2 microcontroller family products. Other derivates of the V850 series can also be supported by minor changes
of the source code. The AD conversion is done using the dual slope method. It is performed with a minimum of external hardware components. Only three resistors and one capacitor are needed.
Application Note U17227EE1V0AN00
7
Chapter 2 Description of A/D Conversion Using the Dual Slope Method
Using the dual slope method a resistor value can be converted into a digital counter value.
To do this, the charging time of a capacitor will be measured with a timer of a microcontroller. The first
charging slope will use a reference resistor (RREF) and the second charging slope will use variable
resistor or thermistor (RVAR) which should be determined. By the comparison of the two measured
times and the known reference resistor (RREF) the variable resistor (RVAR) can be calculated.
The V850ES / Fx2 family has the advantage of bit settable I/O ports and Schmitt-trigger inputs (e.g.
P32/TIP00). In this application the bit settable port P3 is used as a bidirectional port.
At first, the port P32/TI00 is cleared and set to output mode. In this case the capacitor is discharged
and prepared for the first measurement. The resistor RP is only used to limit the current during the discharging of the capacitor. Then port P33 is set to 1 and output. At this point also the 16-bit capture timer
is started. The rest of the port P3 is set to input (high impedance). So the capacitor will be charged via
the reference resistor RREF. When the capacitor has reached the threshold level of the
Schmitt-trigger input P32/TIP00, the actual timer value is automatically captured and an internal interrupt is generated. Using this interrupt the capture value is read out. Now the capacitor will be discharged again. The same procedure starts once more with port P34. This time the capacitor is charged
via the unknown resistor RVAR and after the threshold is reached again the second timer value is read
out.
The unknown RVAR can be calculated from the two values obtained using the method described above
and the value of the reference resistor. (Please refer to derivation.)
8
Application Note U17227EE1V0AN00
Chapter 3 Derivation
–
RREF : V CREF = V DD 1 - e
–
RVAR : V CVAR = V DD 1 - e
tRE F
RR E F × C
tVAR
RVAR × C
VC = VCVAR = VCREF = const
The threshold level of the Schmitt-trigger input does not have any influence on the accuracy of the
measurement. As this will be a constant for both measurements.
–
V DD 1 - e
tRE F
RR E F × C
–
1-e
–
e
–
= V DD 1 - e
tRE F
RR E F × C
–
=1-e
tRE F
RR E F × C
tRE F
RR E F × C
tRE F
RR E F
RVAR
–
=e
=
=
=
tVAR
RVAR × C
tVAR
RVAR × C
tVAR
RVAR × C
tVAR
RVAR × C
tVAR
RVAR
RREF ×
tREF
tVAR
C and VDD do not have any influence on the accuracy of the measurement. Only the absolute value of
the reference resistor RREF has an influence, because these parameters will not change during one
measurement. Using the RREF, tREF and tVAR, the resistor RVAR can be calculated.
Application Note U17227EE1V0AN00
9
Chapter 4 Circuit Diagram
Figure 4-1:
Circuit Diagram
µPD70F3239
to send the data to a PC
P30/TXDA0
P34
P33
R VAR
R REF
RP
P32 / TIP00 (Timer 0 Input 0)
C
10
Application Note U17227EE1V0AN00
Chapter 5 Hardware
Port P33 is used to charge the capacitor via the reference resistor RREF. Port P34 is used to charge the
capacitor via the unknown resistor RVAR. The time of charging the capacitor is measured in both cases.
Port 32 / TIP00 is used as a capture input for the timer. This port has a Schmitt-trigger behaviour. Additionally this port is used to discharge the capacitor. The protection resistor RP will limit the discharging
current and must be considered for the discharge time.
Port 30 is used as output. This pin is shared with the transmit pin of the UARTA, and used to send the
measured data to a PC (terminal program).
5.1 Calculation of Charging Time and Timer Setup
5.1.1 Charging time
V C = V DD 1 - e
VC
= 1-e
V DD
VC
=e
1V DD
-
t
R×C
t
R×C
t
R×C
V
t
= ln 1 - C
V DD
R×C
t = - R × C × ln 1 -
VC
V DD
Example:
VDD = 5 V; Vthreshold = VC = (0.4 …0.7) VDD
Typical Vthreshold = 0.6 VDD
RREF = 51 KΩ; C = 220 nF
RP = 100 Ω
t = - RREF × C × ln (1-VC/VDD)
tTYP = -51 KΩ × 220 nF × ln (1 - 0.6)
tTYP = 10.28 ms
Application Note U17227EE1V0AN00
11
Chapter 5
Hardware
5.1.2 Timer setup
Max setup time:
tMAX
= -51 KΩ × 220 nF × ln (1 - 0.7)
tMAX
= 13.5 ms
Resolution:
Resolution = tMAX / step time
With the 16-bit capture timer of the V850ES / Fx2 family a resolution of 50 ns (fXX @20 MHz) can be
realized. Thus the reached resolution will be:
Resolution = tMAX / 50 ns
= 13.5 ms / 50 ns
= 270.000 steps
This amount of steps would generate an overflow of the 16-bit timer (65536 steps). So, the timer prescaler is set to a resolution of 200 ns (fXX/4 @20 MHz).Then the reached resolution will be:
Resolution = tMAX / 200 ns
= 13.5 ms / 200 ns
= 67.500 steps
Thus in this application note a resolution of about 16 bit is used. Due to the max timer resolution of
16-bit (65536 steps) a higher or a lower resolution can be realized by changing the timer prescaler or
the setup time.
Note: It is recommended that the value of the resistors RREF and RVAR should be in a range between
10 KΩ and 100 KΩ.
Lower resistors than 10 KΩ may result a lower accuracy due to the voltage drop (VOH = f (IOH)).
Higher resistor values than 100 KΩ might cause a lower accuracy due to some leakage current.
12
Application Note U17227EE1V0AN00
Chapter 6 Software
The software consists of the following three modules.
6.1 Main
This module contains the system initialization and the main loop.
CPU clock, all ports, the used 16-bit timer and the UART will be initialized. In the main loop the conversion is started, the result converted and the transmission module was called.
6.2 Measurement
This module will do a complete dual slope measurement.
This is in detail:
• Discharging the capacitor.
• Reference measurement using RREF.
• Store the result for the reference resistor.
• Discharging the capacitor.
• Absolute measurement using RVAR.
• Store the result for the variable resistor.
6.3 Data Transmission
This module converts the measured data to an ASCII format and sends it via UART. Using this module
the measured data can be displayed on a PC using a terminal program.
Application Note U17227EE1V0AN00
13
Chapter 7
Software Flowcharts
7.1 Main Routine
Figure 7-1:
Main Flow
Start
Hardware initialization
Start measurement
Finished ?
No
Yes
Convert result
Call data transmission
End
14
Application Note U17227EE1V0AN00
Chapter 7
Software Flowcharts
7.2 Measurement Function
Figure 7-2:
Measurement Flow
Measure
Discharge the capacitor
Charge capacitor via R REF
and start capture timer
Saturated ?
No
Yes
Store reference counter value
Discharge the capacitor
Charge capacitor via R VAR
and start capture timer
Saturated ?
No
Yes
Store variable counter value
End
Application Note U17227EE1V0AN00
15
Chapter 7
Software Flowcharts
7.3 Data Transmission
Figure 7-3:
Data Transmission Flow
Data transmission
Convert HEX to ASCII
Transmit the data via UART
End
16
Application Note U17227EE1V0AN00
Chapter 8 Listing
/*==============================================================
** PROJECT
= Dual_Slope.c
** MODULE
=
** VERSION
= 0.0
** DATE
= 3.05.2004
** LAST CHANGE =
**==============================================================
** Description: Demoprorgam for dual slope emulation
**
**==============================================================
** Enviroment: Device:
uPD70F3239
**
C-Compiler:
Green Hills
Version 3.5.1
**
**==============================================================
** By:
NEC Electronics (Europe) GmbH
**
Arcadia Strasse 10
**
D-40472 Duesseldorf
**
**
NEC-EE, CES
**==============================================================
Changes:
**==============================================================
*/
/*==============================================================
** include
**==============================================================
*/
#include "df3239.h"
#include "df3239extIO.h"
/*==============================================================
** type definitions
**==============================================================
*/
typedef enum { false = 0, true = 1 } bit;
/*==============================================================
** definitions
**==============================================================
*/
/* Reference resistor value */
#define REF_RESISTOR
56000
/* Loop constant for discharging C */
#define WAITLOOP
2000
/* macros for portpin switching
#define TM_PORT
#define TM_PORT_MODE
#define TM_PORT_MODE_CONTROL
#define REF_PORT
#define REF_PORT_MODE
*/
((volatile
((volatile
((volatile
((volatile
((volatile
struct
struct
struct
struct
struct
Application Note U17227EE1V0AN00
bitf
bitf
bitf
bitf
bitf
*)(&P3))->bit02
*)(&PM3))->bit02
*)(&PMC3))->bit02
*)(&P3))->bit03
*)(&PM3))->bit03
17
Chapter 8
#define VAR_PORT
#define VAR_PORT_MODE
Listing
((volatile struct bitf *)(&P3))->bit04
((volatile struct bitf *)(&PM3))->bit04
/* macros for starting and stopping the timer */
#define Timer_Start()
(((volatile struct bitf *)&(TP0CTL0))->bit07 = 1)
#define Timer_Stop()
(((volatile struct bitf *)&(TP0CTL0))->bit07 = 0)
/* State machine defines for timer ISR */
#define DISCHARGE_STATE
0
#define REF_CONV_STATE
1
#define MEASUREMNT_STATE
2
/*=============================================================
** variable definitions
**=============================================================
*/
unsigned int
ref_time, meas_time, calc_value;
unsigned char
DS_status;
bit
DS_Ready, DS_OVF_error, sendokflag;
/* --------------------------------------------------------------------- */
/* Hardware initialization
*/
/* --------------------------------------------------------------------- */
void hdwinit (void) {
/* Basic configuration for µPD70F323x */
VSWC
= 0x01;
/* Peripheral wait states as recommended in manual */
PRCMD
PCC
WDTM2
RCM
PLLCTL
= 0x00;
= 0x00;
= 0x1f;
= 0x01;
= 0x03;
/* Prepare to write specific register */
/* Select cpu clock fxx = foscl
*/
/* Stop watchdog timer
/* Stop ring oscillator
/* F-Line CPUs have a PLL -> fxx = Osc_Freq * 4
/* Port setting; Set all unused port to output to avoid floating */
PM0
= 0x00;
PM1
= 0x00;
PM3H
= 0x00;
PM4
= 0x00;
PM5
= 0x00;
PM6
= 0x0000;
PM7L
= 0x00;
PM7H
= 0x00;
PM8
= 0x00;
PM9
= 0x0000;
PM12
= 0x00;
PMDL
= 0x0000;
PMCS
= 0x00;
PMCT
= 0x00;
PMCM
= 0x00;
PMCD
= 0x00;
18
Application Note U17227EE1V0AN00
*/
*/
*/
Chapter 8
Listing
/* Configure ports for dualslope */
P3L
= 0x0C;
/* REF_PORT, VAR_PORT =1; TM_PORT=0 */
PM3L
= 0xFA;
/* REF_PORT, VAR_PORT =input; TM_PORT=output */
PMC3L = 0x01;
/* TXDA0 output; TM_PORT=I/O(not peripheral) */
PFC3L = 0x00;
/* P32 = TIP00 */
PFCE3L = 0x04;
/*
"
*/
/* 16-bit timer setting */
//TP0CTL0 = 0x01; /* fxx/2
*/
//TP0CTL0 = 0x02; /* fxx/4
*/
TP0CTL0 = 0x03;
/* fxx/8
*/
//TP0CTL0 = 0x04; /* fxx/16 */
//TP0CTL0 = 0x05; /* fxx/32 */
//TP0CTL0 = 0x06; /* fxx/64 */
//TP0CTL0 = 0x07; /* fxx/128 */
TP0CTL1 = 0x05;
/* Free running mode */
TP0IOC0 = 0x00;
/* No output */
TP0IOC1 = 0x01;
/* Rising edge input */
TP0IOC2 = 0x00;
/* No edge detection */
TP0OPT0 = 0x10;
/* TP0CCR00 as capture register */
TP0CCIC0 = 0x00; /* Enable Timer P0 capture int. 0; Priority 0 */
TP0OVIC = 0x00; /* Enable Timer P0 overflow err. int.; Priority 0 */
/*UARTA0 setting */
UA0CTL0 = 0xD2; /* Enable,Trans.,LSB first,8bit,no parity,1stop */
UA0CTL1 = 0x02; /* 38400 bps @ 20 MHz Error: 0.16% */
UA0CTL2 = 65;
/*
"
*/
UA0TIC = 0x07; /* Enable transmit interrupt; priority 7 (lowest) */
}
/* --------------------------------------------------------------------- */
/* Discharging capacitor for starting measurement
*/
/* --------------------------------------------------------------------- */
void discharge_C (void) {
unsigned int i;
REF_PORT_MODE
VAR_PORT_MODE
= 1;
= 1;
/* Switch reference port to Hi-z(Input)*/
/* Switch variable port to Hi-z(Input) */
TM_PORT_MODE_CONTROL = 0; /* Switch port pin to I/O
*/
TM_PORT
= 0; /* Switch port pin to 0 -> Discharge C */
for (i=0;i<WAITLOOP;i++) { /* Wait for discharging the capacitor
__asm("nop");
/*
Waste time ...
}
*/
*/
TM_PORT_MODE_CONTROL = 1;
*/
/* Switch port pin to timer input
}
/* --------------------------------------------------------------------- */
/* Send data via UARTA0 as decimal value
*/
/* --------------------------------------------------------------------- */
void senddata(unsigned int data) {
sendokflag = false;
UA0TX = ':';
while (sendokflag == false);
Application Note U17227EE1V0AN00
19
Chapter 8
Listing
sendokflag = false;
UA0TX = ((data/100000)%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = ((data/10000)%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = ((data/1000)%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = '.';
/* decimal point -> xxx.xxx */
while (sendokflag == false);
sendokflag = false;
UA0TX = ((data/100)%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = ((data/10)%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = (data%10)+'0';
while (sendokflag == false);
sendokflag = false;
UA0TX = 0x0D;
while (sendokflag == false);
}
/* --------------------------------------------------------------------- */
/* Send data via UARTA0 as decimal value
*/
/* --------------------------------------------------------------------- */
void sendstring(const char *str) {
while (*str) {
sendokflag = false;
UA0TX = *str++;
while (sendokflag == false);
}
}
/* --------------------------------------------------------------------- */
/* UARTA0 transmission end interrupt service routine
*/
/* --------------------------------------------------------------------- */
__interrupt void INTUA0T(void) {
sendokflag = true;
}
/* --------------------------------------------------------------------/* Timer P0 overflow interrupt service routine
/*
State machine for dualslope measurement
/* --------------------------------------------------------------------__interrupt void INTTP0OV(void) {
Timer_Stop();
/* Stop and clear timer
*/
DS_OVF_error = true;
/* Set overflow error flag
*/
DS_Ready
= true;
/* Indicate end of conversion
*/
}
20
Application Note U17227EE1V0AN00
*/
*/
*/
*/
Chapter 8
Listing
/* --------------------------------------------------------------------/* Timer P0 capture 0 interrupt service routine
/*
State machine for dualslope measurement
/* --------------------------------------------------------------------__interrupt void INTTP0CC0(void) {
unsigned int CR_value;
CR_value = TP0CCR0;
Timer_Stop();
*/
*/
*/
*/
/* Read captured timer value */
/* Stop and clear timer
*/
switch(DS_status) {
case DISCHARGE_STATE:
/* Start of reference measurement */
discharge_C();
/*
Discharging C */
REF_PORT
= 1;
/*
Set ref. resistor port to high */
REF_PORT_MODE = 0;
/*
"
*/
Timer_Start();
/*
Start timer */
DS_status = REF_CONV_STATE;
break;
case REF_CONV_STATE:
/* Start of 2. conversion */
ref_time = CR_value;
discharge_C();
/*
Discharging C */
VAR_PORT
= 1;
/*
Set var. resistor port to high */
VAR_PORT_MODE = 0;
/*
"
*/
Timer_Start();
/*
Start timer */
DS_status = MEASUREMNT_STATE;
break;
case MEASUREMNT_STATE:
/* End of dualslope conversion */
meas_time
= CR_value;
VAR_PORT_MODE = 1;
/*
Var. res. port to Hi-z(Input)*/
DS_Ready
= true; /*
Conversion finished */
break;
}
}
/* ===================================================================== */
/* main function
*/
/* ===================================================================== */
void main(void) {
//DI();
hdwinit ();
EI();
/* Interrupt disable
*/
/* Peripheral settings */
/* Interrupt enable
*/
/* Initialize dual-slope flags and status-counter */
DS_status
= DISCHARGE_STATE;
DS_Ready
= false;
DS_OVF_error = false;
/* Start conversion by enabling the timer interrupt
*/
/* and setting the interrupt flag; Priority 0 (highest) */
Application Note U17227EE1V0AN00
21
Chapter 8
Listing
TP0CCIC0 = 0x80;
while(1) {
/* Endless loop - Main loop */
if (DS_Ready) { /* Conversion finished */
if (DS_OVF_error == false) {
/* Calculate value here reference resistor = 51k */
calc_value = REF_RESISTOR * meas_time / ref_time;
/* Send data via UART */
senddata(calc_value);
} else {
/* Timer overflow error */
if (DS_status == REF_CONV_STATE)
sendstring("Reference error\r");
else /* DS_status == MEASUREMNT_STATE */
sendstring("Measurement error\r");
}
/* Initialize dual-slope flags and status-counter */
DS_status
= DISCHARGE_STATE;
DS_Ready
= false;
DS_OVF_error = false;
/* Start conversion */
TP0CCIC0 = 0x80;
}
/* . . .
*/
/* Do anything while conversion is in background progress ... */
/* . . .
*/
}
}
22
Application Note U17227EE1V0AN00
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