AN1096

AN1096
Using the C30 Compiler to Interface SPI Serial EEPROMs
with dsPIC33F and PIC24F
This application note provides assistance and source
code to ease the design process of interfacing a
Microchip dsPIC33F Digital Signal Controller to a
Microchip SPI serial EEPROM, without the use of a
hardware serial port.
Martin Kvasnicka
Microchip Technology Inc.
INTRODUCTION
The 25XXX series serial EEPROMs from Microchip
Technology are SPI compatible and have maximum
clock frequencies ranging from 3 MHz to 20 MHz. Many
times when designing an application which utilizes a
serial EEPROM device, it may be beneficial to use a
microcontroller which does not feature a dedicated
protocol-specific serial port. This can be due to several
possible reasons, including size restrictions or costs. In
these instances, it is required of the designer to write
software routines capable of generating the proper
signals for communicating with the EEPROM device.
FIGURE 1:
Figure 1 describes the hardware schematic for the
interface between Microchip’s 25XXX series devices
and the dsPIC33F DSC or PIC24F PIC® microcontroller. The schematic shows the connections necessary
between the DSC or PIC MCU and the serial EEPROM
as tested, and the software was written assuming
these connections. The WP and HOLD pins are tied to
VCC through resistors, because the write-protect and
hold features are not used in the examples provided.
CIRCUIT FOR dsPIC33F256GP710, PIC24FJ128GA010 AND 25XXX SERIES
DEVICES
100 Pin TQFP
VSS
VDD
U1CTS/CN20/RD14
U1RTS/CN21/RD15
U2RX/CN17/RF4
U2TX/CN18/RF5
dsPIC33FJ256GP710
PIC24FJ128GA010
SDA1/RG3
SCK1/INT0/RF6
SDI1/RF7
SDO1/RF8
U1RX/RF2
U1TX/RF3
Vcc
CS
1
SO
2
WP
3
Vss
4
25XXX
Author:
8
Vcc
7
HOLD
6
SCK
5
SI
Note: CS, WP and HOLD pins should all have pull-up resistors (~10k-ohms).
© 2007 Microchip Technology Inc.
DS01096B-page 1
AN1096
FIRMWARE DESCRIPTION
The purpose of the program is to show individual
features of the SPI protocol and give code samples of
the instructions and addressing schemes so that the
basic building blocks of a program can be shown. The
firmware performs the following operations:
•
•
•
•
•
•
Low-Density Byte Write
Low-Density Byte Read
Low-Density Page Write
Low-Density Sequential Read
Write Enable
WIP Polling
In addition, the following operations are available but
not explicitly illustrated:
•
•
•
•
•
•
•
High-Density Byte Write
High-Density Byte Read
High-Density Page Write
High-Density Sequential Read
Write Disable
Read Status Register
Write Status Register
The low-density routines are intended for use with the
4K and smaller density devices that use only one byte
for addressing. The high-density routines are intended
for use with 8K and higher density devices that use two
bytes for addressing. This program also exhibits the
WIP polling feature for detecting the completion of write
cycles after the byte write and page write operations.
Read operations are located directly after each write
operation, thus allowing for verification that the data
was properly written. No method of displaying the input
data is provided, but a SEEVAL® 32 evaluation system,
an oscilloscope, or a Microchip MPLAB® ICD 2 could
be used.
The low-density code was tested using the
25LC040A serial EEPROM. This device features 512
x 8 (4 Kbit) of memory and 16-byte pages. The highdensity code was tested using the 25LC256 serial
EEPROM. This device features 32K x 8 (256 Kbit) of
memory and 64-byte pages. Only the low-density
operations are illustrated in this application note.
Oscilloscope screen shots are labeled for ease in reading. The data sheet versions of the waveforms are
shown below the oscilloscope screen shots. All timings
are designed to meet the data sheet specs, and an 8
MHz crystal oscillator is used to clock the dsPIC33F
DSC or PIC24F microcontroller. If a different clock is
used, the code may need to be modified to avoid violating timing specs. All values represented in this application note are decimal values unless otherwise noted.
DS01096B-page 2
© 2007 Microchip Technology Inc.
AN1096
WRITE ENABLE
a write is attempted to either the array or the STATUS
register. The WEL bit can be cleared by issuing a Write
Disable command (WRDI) and is also automatically
reset if the device is powered down or if a write cycle is
completed.
Figure 2 shows an example of the Write Enable
command. Chip Select is brought low (active) and the
opcode (0x06) is shifted out. The Write Enable command must be given in order to set the WEL bit before
FIGURE 2:
WRITE ENABLE (WREN)
CS
0
1
2
3
4
5
6
7
SCK
SI
SO
© 2007 Microchip Technology Inc.
0
0
0
0
0
1
1
0
High-Impedance
DS01096B-page 3
AN1096
READ STATUS REGISTER TO CHECK
FOR WEL BIT
The STATUS register is shifted out on the Serial Out
pin. A value of 0x02 shows that the WEL bit in the
STATUS register has been set. The device is now
ready to do a write to either the STATUS register or the
array.
Figure 3 shows an example of the Read Status
Register command to check for the WEL bit. This bit
must be set before a write is attempted to either the
STATUS register or the array. It is good programming
practice to check for the bit to be set before attempting
the write. Once again the device is selected and the
opcode (0x05) is sent.
FIGURE 3:
READ STATUS REGISTER TO CHECK FOR WEL BIT (RDSR)
CS
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
0
SCK
Instruction
SI
0
0
0
0
0
High-Impedance
SO
DS01096B-page 4
1
0
1
Data from STATUS register
7
6
5
4
3
2
© 2007 Microchip Technology Inc.
AN1096
BYTE WRITE COMMAND (OPCODE,
ADDRESS AND DATA)
Figure 4 shows an example of the Write command.
First, the device is selected by bringing Chip Select low
(active). In this example, the Most Significant bit of the
address is a ‘1’. This bit is embedded in the opcode
(0x02 for a Write command), and so the value, 0x0A, is
sent. The Low Address byte (0x33) is sent next. Finally,
the data is clocked in, in this case, 0xCC. Once Chip
Select is toggled at the end of this command, the internal write cycle is initiated. After the write cycle has
begun, the WIP bit in the STATUS register can be
polled to check when the write finishes. If polling is not
used, a delay (~5ms) needs to be added to ensure the
write has finished. This code uses WIP polling.
FIGURE 4:
A page write can be accomplished by continuing to
send data bytes to the device without toggling CS. Up
to 16 bytes can be written to the 25LC040A before a
write cycle is needed. Once CS is brought high after the
data bytes have been transmitted, then the write cycle
timer will begin and normal polling can be initiated.
The Page Write function provided in the firmware is
used to program 16 bytes of data, starting at address
0x150. Because page writes cannot cross page boundaries, care must be taken to avoid having data wrap
around to the beginning of the page and overwrite
existing data.
BYTE WRITE COMMAND, ADDRESS AND DATA
CS
TWC
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
SCK
Instruction
SI
0
0
0
0
A8
Data Byte
Low Address Byte
0
1
0
A7 A6 A5 A4 A3 A2 A1 A0
7
6
5
4
3
2
1
0
High-Impedance
SO
© 2007 Microchip Technology Inc.
DS01096B-page 5
AN1096
DATA POLLING (RDSR – CHECK FOR
WIP SET)
case, the device is selected and the RDSR opcode
(0x05) is sent. The STATUS register is then shifted out
on the Serial Out (SO) pin resulting in a value of 0x03.
Figure 5 shows that both the WEL bit (bit 1) and the
WIP bit (bit 0) are set, meaning that the write cycle is in
progress.
After a valid Write command is given, the STATUS
register can be read to check if the internal write cycle
has been initiated, and it can continuously be
monitored to look for the end of the write cycle. In this
FIGURE 5:
DATA POLLING (READ STATUS REGISTER TO CHECK WIP BIT)
CS
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
0
SCK
Instruction
SI
0
0
0
0
0
High-Impedance
SO
DS01096B-page 6
1
0
1
Data from STATUS register
7
6
5
4
3
2
© 2007 Microchip Technology Inc.
AN1096
DATA POLLING FINISHED
(RDSR – WIP BIT CLEARED)
The firmware remains in a continuous loop and the WIP
status is evaluated until the bit is cleared. Figure 6
shows the Read Status Register command followed by
a value of 0x00 being shifted out on the Serial Out (SO)
pin. This indicates that the write cycle has finished and
the device is now ready for additional commands. The
WEL bit is also cleared at the end of a write cycle,
which serves as additional protection against
unwanted writes.
FIGURE 6:
DATA POLLING FINISHED (RDSR – WIP AND WEL BITS CLEARED)
CS
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
0
SCK
Instruction
SI
0
0
0
0
0
High-Impedance
SO
© 2007 Microchip Technology Inc.
1
0
1
Data from STATUS register
7
6
5
4
3
2
DS01096B-page 7
AN1096
READ COMMAND (OPCODE,
ADDRESS AND DATA)
Figure 7 shows an example of the Read command. For
this, the device is selected. As with the Write command,
the Most Significant bit of the address is a ‘1’. Therefore, when combined with the Read opcode (0x03), the
value 0x0B is sent. The Low Address byte, 0x33, is
FIGURE 7:
then sent. Finally the data, 0xCC in this case, is clocked
out on the Serial Out (SO) pin. In order to perform a
sequential read, more clocks need to be generated. It
is possible to read the entire chip by continuing to clock
the device. Once the end of the array is reached, the
data will wrap to the beginning of the array (address
0x000) and keep reading out until CS is deselected or
the device is no longer being clocked.
READ COMMAND, ADDRESS AND DATA
CS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
SCK
Instruction
SI
0
0
0
0
A8
Low Address Byte
0
1
1
A7 A6 A5 A4 A3 A2 A1 A0
Don’t Care
Data Out
High-Impedance
SO
DS01096B-page 8
7
6
5
4
3
2
1
0
© 2007 Microchip Technology Inc.
AN1096
CHANGING PROCESSORS
CONCLUSION
This application note code was written to simplify
changing between processors. There are, however, a
couple of steps that need to be taken in order to do this.
This application note was tested with two specific
processors, the dsPIC33FJ256GP710 and the
PIC24FJ128GA010. If you are going to use processors
that are different from these two, please consult the
device-specific data sheet to check for any other potential issues when using this code. As mentioned previously, the Explorer 16 development board was used for
this application note with the connections shown in
Figure 1. In order to change between these processors
there are four steps:
These are some of the basic features of SPI communications on one of Microchip’s dsPIC33F or PIC24F
devices without the use of a hardware serial port. The
code is highly portable and can be used on many
dsPIC® DSCs with very minor modifications. Using the
code provided, designers can begin to build their own
SPI libraries to be as simple or as complex as needed.
The code was tested on Microchip’s Explorer 16
Demonstration Board with the connections shown in
Figure 1.
1.
2.
3.
4.
The current processor module currently on the
Explorer 16 board must be physically replaced
with the processor module desired. Be sure to
disconnect power during this procedure.
The #define statements on lines 42 and 43 in the
an1096.h file must be commented in/out for the
desired processor.
The new processor needs to be selected in the
MPLAB IDE by going to Configure>Select
Device...
The linker file needs to be added/removed for
the desired processor. If this is not done, it will
not prevent the code from compiling but may
create some undesired warnings from the
compiler.
© 2007 Microchip Technology Inc.
DS01096B-page 9
AN1096
NOTES:
DS01096B-page 10
© 2007 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, Accuron,
dsPIC, KEELOQ, KEELOQ logo, microID, MPLAB, PIC,
PICmicro, PICSTART, PRO MATE, rfPIC and SmartShunt are
registered trademarks of Microchip Technology Incorporated
in the U.S.A. and other countries.
AmpLab, FilterLab, Linear Active Thermistor, Migratable
Memory, MXDEV, MXLAB, SEEVAL, SmartSensor and The
Embedded Control Solutions Company are registered
trademarks of Microchip Technology Incorporated in the
U.S.A.
Analog-for-the-Digital Age, Application Maestro, CodeGuard,
dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONITOR, FanSense, FlexROM, fuzzyLAB,
In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi,
MPASM, MPLAB Certified logo, MPLIB, MPLINK, PICkit,
PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal,
PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, Select
Mode, Smart Serial, SmartTel, Total Endurance, UNI/O,
WiperLock and ZENA are trademarks of Microchip
Technology Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2007, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received ISO/TS-16949:2002 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
© 2007 Microchip Technology Inc.
DS01096B-page 11
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DS01096B-page 12
© 2007 Microchip Technology Inc.
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