Fujitsu Microelectronics Europe
Application Note
MCU-AN-390105-E-V11
F²MC-8L/16LX FAMILY
8/16-BIT MICROCONTROLLER
MB90340
SPI COMMUNICATION TO
EXTERNAL ADC
(for MAX1286)
APPLICATION NOTE
SPI COMMUNICATION TO ADC
Revision History
Revision History
Date
2003-05-28
2010-06-11
Issue
V1.0; MWi, first version
V1.1; MWi, CPHA, CPOL logic corrected
This document contains 14 pages.
MCU-AN-390105-E-V11
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Warranty and Disclaimer
Warranty and Disclaimer
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starter kits, schematics, engineering samples of IC’s etc.) is subject to the conditions of Fujitsu
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the Sale and Purchase Agreement under which agreements the Product has been delivered, (ii) the
technical descriptions and (iii) all accompanying written materials.
Please note that the deliverables are intended for and must only be used for reference in an
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The software deliverables are provided on an as-is basis without charge and are subject to
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The contents of this document are subject to change without a prior notice, thus contact FME about
the latest one.
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Contents
Contents
REVISION HISTORY.............................................................................................................. 2
WARRANTY AND DISCLAIMER............................... ERROR! BOOKMARK NOT DEFINED.
CONTENTS ............................................................................................................................ 3
0 INTRODUCTION................................................................................................................ 5
1 MAX1286 ........................................................................................................................... 6
1.1
ADC .......................................................................................................................... 6
1.2
Connection to MB90340............................................................................................ 6
1.3
Communication Timing ............................................................................................. 7
1.4
1.3.1
Read Cycle Timing of MAX1286 ................................................................. 7
1.3.2
“X-Bits” at end of communication ................................................................ 7
Example Code .......................................................................................................... 8
1.4.1
1.4.2
1.4.3
Initial Functions and Declarations ............................................................... 8
1.4.1.1
Flowchart .................................................................................... 8
1.4.1.2
C Code........................................................................................ 9
Read Data from ADC ................................................................................ 10
1.4.2.1
Flowchart .................................................................................. 10
1.4.2.2
C Code...................................................................................... 11
Example of usage of Get_ADC function in Main Function ........................ 12
1.4.3.1
Flowchart .................................................................................. 12
1.4.3.2
C Code...................................................................................... 13
2 BIBLIOGRAPHY.............................................................................................................. 14
2.1
Related Documents................................................................................................. 14
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Introduction
0 Introduction
This application note describes how to communicate via SPI using the MB90340-UART with
an external ADC. In this note a MAX1286 from Maxime is used.
Please note, that this document only gives a rough overview about the communication. The
described source codes were written for understanding not for code size or speed. Neither
interrupts nor timer were used. Time critical program code is always performed by simple
flag polling or wait loops.
Please also refer to the Application Note MCU-AN-300002-E-SPI for further SPI specification
and nomenclature.
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1 MAX1286
THIS CHAPTER DESCRIBES HOW TO COMMUNICATE WITH THE MAX1286 ADC
1.1
ADC
The MAX1286 is a 150ksps, 12-Bit, 2-Channel Single-ended ADC.
The MAX1286 has the following pin-out:
•
Vcc 1
8 SCLK
AIN1 2
7 DOUT
AIN2 3
6 CNVST
GND 4
5 REF
Pin names:
Vcc
AIN1
AIN2
GND
SCLK
DOUT
CNVST
REF
1.2
Power Supply (+ 5 volts)
Analog Input Channel 1
Analog Input Channel 2
Ground
Serial Clock Input
Serial Data Output
Conversion Start Input
External Reference Voltage Input
Connection to MB90340
The ADC can be connected as in the following schematic. Please note, that no power supply
pins and other MCU-Pins are drawn than those for the connection to the ADC.
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.3
Communication Timing
Detailed description of the timing and timing parameters can be found in the corresponding
datasheet of the MAX1286 ADC.
1.3.1 Read Cycle Timing of MAX1286
A read cycle (read Channel 1 from ADC) has the following bit timing (SPI-CPOL = 0, SPICPHA = 0):
~3Ms
CNVST
SCK
DOUT
D7
D6
D5
D4
D3
D2
D1
D0
The CNVST signal is performed by Port-Pin. The ADC conversion time is about 3 Ms. After
this time reading from the ADC is allowed. Data sampling of the UART is performed at the
rising edge of the SCK signal.
1.3.2 “X-Bits” at end of communication
Because the ADC has a resolution of 12 bits and the UART can only read 8 bit frames
synchronously, the read-out frame is 16 bit. The ADC sets the MSB of the 12 bit conversion
data to the first bit. Because of this the last read 4 bits are not valid.
SCK from UART
1st 8 Bits
DOUT (SIN0)
D11
D10 D9
D8
D7
2nd 8 Bits
D6
D5
D4
D3
D2
D1 D0
X
X
X
X
Therefore the read-out data has to be shifted 4 times right. The upper 4 bits have to be filled
with “0” then.
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4
Example Code
The following code shows how to establish a SPI communication to the ADC.
1.4.1
Initial Functions and Declarations
1.4.1.1 Flowchart
InitUART
InitPorts
wait
Set Baud rate
Set Port-Register
9 to “0x00”
Argument: j
Set clock inversion
(ESCR-SCES = 1)
Set clock delay
(ECCR-SCDE = 1)
Reception and
Transmission enable
Set Port 90 to
Output for
CNVST-Pin
Do loop
from “0” to “j”
Init Port 0 for LED
bargraph
Set Mode 2, enable
SCLK, enable SOT
Set MSB first
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4.1.2 C Code
void InitUART(void)
{
BGR0 = 15;
ESCR0 = 0x01;
ECCR0 = 0x10;
SCR0 = 0x03;
SMR0 = 0x83;
SSR0 = 0x04;
}
void InitPorts(void)
{
// Bit#0: CNVST
PDR9 = 0x00;
DDR9 = 0x01;
PDR0 = 0x00;
DDR0 = 0xFF;
//
//
//
//
//
//
1M Bit/s @ 16 MHz
SCES = 1 => CPOL = 0
SCDE = 1 => CPHA = 0
reception and transmission enable
Mode 2, SCLK enable, SOT enable
MSB first, no interrupts
// All Low
// P90 = CNVST (Start convert)
// LED-Port on Flash-CAN-100P-340
}
void wait(unsigned char a)
{
unsigned char i;
for(i = 0; i <
a; i++);
}
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4.2
Read Data from ADC
1.4.2.1 Flowchart
Get_ADC
Set CNVST=1 (PDR90 =1)
Wait for 4 NOPs
Set CNVST=0 (PDR90 =0)
Wait for 5 Ms
Write dummy data to produce SCK
Y
RDRF == 0 ?
N
Read reception data and shift left 4 times
Write dummy data to produce SCK
Y
RDRF == 0 ?
N
Read reception data and shift right 4 times and “OR”
it to the last data
Return data to caller
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4.2.2 C Code
unsigned int Get_ADC(void)
{
unsigned int data;
PDR9 = 0x01;
#pragma asm
NOP
NOP
NOP
NOP
#pragma endasm
// Start convert
PDR9 = 0x00;
wait(1);
// Conversion Time (5 Fs approx.)
TDR0 = 0x00;
// Set dummy data to produce SCK
while (SSR0_RDRF == 0);
data = (RDR0 << 4);
// Read bits 11-4
TDR0 = 0x00;
// Set dummy data to produce SCK
while (SSR0_RDRF == 0);
data |= (RDR0 >> 4); // Read bits 3-0
return data;
}
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4.3
Example of usage of Get_ADC function in Main Function
1.4.3.1 Flowchart
main
Call InitPorts
Call InitUART
Call Get_ADC
Use upper 8 bits of ADC
data and put result to the
LEDs of the Starterkit Board
(as bar graph)
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© Fujitsu Microelectronics Europe GmbH
SPI COMMUNICATION TO ADC
Chapter 1 MAX1286
1.4.3.2 C Code
void main(void)
{
unsigned int adc;
unsigned char data;
InitPorts();
InitUART();
// Initialize CNVST, LEDs
// Init UART for SPI communication
while(1)
{
adc = Get_ADC();
data = ((adc >> 4) & 0xFF);
// bits 11-4
if (data > 227) PDR0 = 0xFF;
else if (data > 198) PDR0 = 0x7F;
else if (data > 170) PDR0 = 0x3F;
else if (data > 142) PDR0 = 0x1F;
else if (data > 113) PDR0 = 0x0F;
else if (data > 85) PDR0 = 0x07;
else if (data > 57) PDR0 = 0x03;
else if (data > 28) PDR0 = 0x01;
else PDR0 = 0x00;
}
}
© Fujitsu Microelectronics Europe GmbH
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SPI COMMUNICATION TO ADC
Chapter 2 Bibliography
2 Bibliography
THIS CHAPTER NAMES THE RELATED DOCUMENTS
2.1
Related Documents
•
MCU-AN-300002-E-SPI
Fujitsu Application Note about SPI Modes
•
DS MAX1286-MAX1289
Maxime data sheet of MAX1286
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© Fujitsu Microelectronics Europe GmbH