AN1069

AN1069
Using C30 Compiler and the SPI Module to Interface EEPROMs
with dsPIC33F and PIC24F
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. The
SPI module available on dsPIC33F Digital Signal
Controller and PIC24F microcontroller provide a very
easy-to-use interface for communicating with the
25XXX series devices. The largest benefit of using the
SPI module is that the signal timings are handled
through hardware rather than software. This allows the
firmware to continue executing while communication is
handled in the background. This also means that an
understanding of the timing specifications associated
with the SPI protocol is not required in order to use the
25XXX series devices in designs.
FIGURE 1:
This application note is intended to serve as a
reference for communicating with Microchip’s 25XXX
series serial EEPROM devices with the use of the SPI
module featured on many dsPIC33F and PIC24F
family devices. Source code for common data transfer
modes is also provided.
Figure 1 describes the hardware schematic for the
interface between Microchip’s 25XXX series devices
and the dsPIC33F DSC or the PIC24F MCU. The
schematic shows the connections necessary between
either controller and the serial EEPROM as tested, and
the software was written assuming these connections.
The WP pin is tied to VCC because the STATUS register write-protect feature is not used in the examples
provided.
CIRCUIT FOR dsPIC33FJ256GP710, PIC24FJ128GA010 AND 25XXX SERIES
DEVICE
100 Pin TQFP
VSS
VDD
IC7/U1CTS/CN20/RD14
IC8/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.
DS01069B-page 1
AN1069
FIRMWARE DESCRIPTION
The purpose of the program is to show individual
features of the SPI protocol and give code samples of
the opcodes so that the basic building blocks of a program can be shown. The firmware was written in C and
the Microchip C30 compiler was used. The opcodes
used in the program are Write Enable (WREN), Write,
Read, and Read Status Register (RDSR) (used in the
program for WIP polling). The oscilloscope pictures
have markers that are shown from CS enable to CS
disable for ease in reading. The data sheet version of
the waveform is below the actual oscilloscope picture.
The SPI module is set up for Mode 0,0 operation. The
code is written in modules and commented so changing modes, speeds, and modifying commands such as
sequential reads and page writes is simple. The values
represented in this application note are all hex values
unless otherwise noted.
Besides the standard SPI libraries supplied with the
C30 compiler, the firmware consists of two .c files
(AN1069.c and AN1069_spi.c), organized into nine
sections.
•
•
•
•
•
•
•
•
•
Initialization
Low Density Byte Write
Low Density Byte Read
Low Density Page Write
Low Density Page Read
High Density Byte Write
High Density Byte Read
High Density Page Write
High Density Page Read
The low density routines are intended for use with the
4K and smaller density devices that use only one byte
of address (25XX010A, 25XX020A, and 25XX040A) 1,
2, and 4 Kbit devices. The Most Significant bit (A8) for
the 25XX040A device resides in the control code,
please refer to the individual data sheet for particulars.
The high density routines are intended for use with 8
Kbit and higher density devices that use two bytes of
address. 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 code was tested using a 25LC256 serial
EEPROM. This device features 32k x 8 (256 Kbit) of
memory and 64-byte pages.
DS01069B-page 2
© 2007 Microchip Technology Inc.
AN1069
INITIALIZATION
TRISF Register
In order to configure the SPI module for SPI mode 0,0,
several key registers on the dsPIC33F DSC or PIC24F
MCU need to be properly initialized.
In order to be properly controlled the CS pin must be
configured as an output. This is done by setting the
respective bit in TRISF to ‘0’ for output. The SCK, SDI
and SDO pins will automatically be configured when
the SPI Enable bit is set.
SPI1STAT STATUS Register (SPI1STAT)
SPI1STAT holds all of the Status bits associated with
the SPI module. The SPI Enable bit (SPIPEN) must be
set in order to enable the serial port.
SPI1 Control Register (SPI1CON1)
SPI1CON1 is one of the Configuration registers for the
SPI module. In SPI mode 0,0, the SMP bit of the register needs to be set for data to be sampled at the end of
the output time. The Clock Polarity Select bit (CKP)
needs to be cleared for Idle state of the clock to be a
low level. The MSTEN bit needs to be set for “Master”
mode. Finally, the Secondary Prescale bits (SPRE) and
the Primary Prescale bits (PPRE) are configured, in
this case, 2:1 (Secondary) and 1:1 (Primary).
SPI1CON2 is used for “framed” SPI support, is not
used in the code here and, therefore, is cleared during
initialization.
© 2007 Microchip Technology Inc.
DS01069B-page 3
AN1069
WRITE ENABLE
Figure 2 shows an example of the Write Enable
command. Chip Select is brought low (active) and the
opcode is sent out through the SPI port. The Write
Enable command must be given before 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) or it is automatically reset if the
device is powered down or a write cycle is completed.
FIGURE 2:
WRITE ENABLE (WREN)
CS
0
1
2
3
4
5
6
7
SCK
SI
SO
DS01069B-page 4
0
0
0
0
0
1
1
0
High-Impedance
© 2007 Microchip Technology Inc.
AN1069
READ STATUS REGISTER TO CHECK
FOR WEL BIT
Once again the device is selected and the opcode,
0x05, is sent. 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. The WEL
bit must be set before a write is attempted to either the
STATUS register or the array. It is good programming
practice to check whether this bit is set before
attempting the write.
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
© 2007 Microchip Technology Inc.
1
0
1
Data from STATUS Register
7
6
5
4
3
2
DS01069B-page 5
AN1069
BYTE WRITE COMMAND (OPCODE,
ADDRESS AND DATA)
Figure 4 shows an example of the Write command. For
this, the device is selected and the opcode, 0x02, is
sent. The High Address byte is given 0x00, followed by
the Low Address byte, 0x10. Finally, the data is clocked
in last, in this case, 0xA5. Once the Chip Select is toggled at the end of this command, the internal write cycle
is initiated. Once the internal write cycle has begun, the
WIP bit in the STATUS register can now be polled to
check when the write finishes or a delay needs to be
added (~5ms), if the WIP bit is not being polled. This
code uses WIP polling.
FIGURE 4:
A page write can be accomplished by continuing to give
data bytes to the device without toggling CS. Up to one
full page (64 bytes for the 25XX256) can be written
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 included page write function programs all
64 bytes of data in the first page. Since the starting
address is 0x0010, the last 16 bytes of data will wrap
from address 0x003F to address 0x0000 and complete
the page. Caution should be taken when initiating
writes in this manner so that previously stored data
doesn’t get overwritten.
BYTE WRITE COMMAND, ADDRESS AND DATA
CS
Twc
0
1
2
0
0
0
3
4
8
5
6
7
9 10 11
0
1
0 15 14 13 12
21 22 23 24 25 26 27 28 29 30 31
SCK
Instruction
SI
0
0
16-bit Address
Data Byte
2
1
0
7
6
5
4
3
2
1
0
High-Impedance
SO
DS01069B-page 6
© 2007 Microchip Technology Inc.
AN1069
DATA POLLING (RDSR – CHECK FOR
WIP SET)
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 case,
the device is selected and the opcode, 0x05, is sent.
The STATUS register is then shifted out on the Data
Out 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 the write cycle is in progress.
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
© 2007 Microchip Technology Inc.
1
0
1
Data from STATUS Register
7
6
5
4
3
2
DS01069B-page 7
AN1069
DATA POLLING FINISHED
(RDSR – WIP BIT CLEARED)
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.
The part remains in a continuous RDSR loop and the
WIP status is evaluated until the bit is cleared. Figure 6
shows the Status Register Read command followed by
a value of 0x00 being shifted out on the Data Out pin.
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
DS01069B-page 8
1
0
1
Data from STATUS Register
7
6
5
4
3
2
© 2007 Microchip Technology Inc.
AN1069
READ COMMAND (OPCODE,
ADDRESS AND DATA)
out on the Serial Out pin, in this case, 0xA5. In order to
do a sequential read, more clocks need to be generated. It is possible to read the entire chip by continuing
to provide clocks to the device. Once the end of the
array is reached, the data will wrap to the beginning of
the array (Address 0x0000) and keep reading out until
CS is deselected or clocks stop being provided.
Figure 7 shows an example of the Read command. For
this, the device is selected and the opcode, 0x03, is
sent. The High Address byte is given 0x00, followed by
the Low Address byte, 0x10. Finally, the data is clocked
FIGURE 7:
READ COMMAND, ADDRESS AND DATA
CS
0
1
2
3
4
5
6
7
8
9 10 11
21 22 23 24 25 26 27 28 29 30 31
SCK
Instruction
SI
0
0
0
0
0
16-bit Address
0
1
1 15 14 13 12
2
1
0
Data Out
High-Impedance
SO
© 2007 Microchip Technology Inc.
7
6
5
4
3
2
1
0
DS01069B-page 9
AN1069
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 using the SPI module on one of Microchip’s
dsPIC33F devices. The code is highly portable and can
be used on many devices that have the SPI module
with very minor modifications. Using the code provided,
designers can begin to build their own SPI libraries to
be as simple or complex as needed. The code was
tested on Microchip’s Explorer 16 Development 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 30 and 31 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 will
remove some undesired warnings from the
compiler.
DS01069B-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
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and may be superseded by updates. It is your responsibility to
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© 2007, Microchip Technology Incorporated, Printed in the
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Printed on recycled paper.
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© 2007 Microchip Technology Inc.
DS01069B-page 11
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DS01069B-page 12
© 2007 Microchip Technology Inc.