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Brush Electronics Bootloaders and File System Drivers for Microchip PIC Controllers.

Software

Software

This page lists some of our software products. In general these products are software tools to faciliate the development of microcontroller systems. All software products available from this site are copyrighted. Please check the licensing conditions carefully. Software from this site cannot be published elsewhere without the express written permission of Brush Electronics.

On this page you can find the following software products:

So you have implemented your first bootloader, performing any hardware and/or processor specific customization for your hardware platform, and want to find out if the bootloader is correctly loading your application. Download this Step-by-Step guide for debugging Brush Electronics' Bootloaders

NOTE our software is licensed to an individual developer. A software license must be purchased for each software developer utilizing this software. The terms and conditions for commercial users and for access to the source code is included in the respective package.

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Paypal does not require the purchaser to have a paypal account and payment can be made with paypal via Visa, Mastercard, etc. When you have paid via PAYPAL please forward a copy of the PAYPAL receipt to sales@brushelectronics.com and include the following software licencing information:

  • the name of the company or individual purchasing the license
  • contact name of license holder
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Once payment has been made via paypal we will receive notification from paypal usually within minutes of the payment being made. Typically the software is emailed the same day payment is received.

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Having problem's with our paypal buttons? Occasionally customers have problems purchasing using these buttons. It is possible to place the order manually at www.paypal.com by making payment to the account sales@brushelectronics.com and, in the comment field, putting the description of the product being purchased. Once you have made the payment, please forward us a copy of the transaction receipt.

SBL - Serial bootloader for the PIC18F series microcontrollers

This serial bootloader is a non encrypting bootloader enabling the remote upgrade of the user application software to the target PIC system via the serial interface. Key attributes of Brush Electronics' Serial Bootloader:

  • Ability to bootload a remote system
  • Incremental Bootloader. As little as a single byte can be modified
  • Suitable for high latency serial links
  • No resources are required on the target PIC other than the flash memory holding the boot code
  • Generic Serial Bootloader User Manual
The package includes the following:
  • Generic Serial Bootloader Source code for the Microchip MPASM assembler or CCS PCH Compiler
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • Encrypted Serial Bootloader User Manual

US $75 SBLA18 - PIC18F Family Generic Serial bootloader - MPASM ASM18
US $75 SBLCCS18 - PIC18F Family Generic Serial bootloader - CCS Compiler


SBLX - Encrypted Serial bootloaders for the PIC18, PIC24/dsPIC33 and PIC32 series microcontrollers

Brush Electronics offers three families of Encrypted Serial Bootloaders for Microchip Microcontrollers. The SBLXCCS18 bootloader supports the PIC18F family and was developed with the CCS PCH compiler. The SBLXC30 bootloader supports the PIC24/dsPIC33 family and was developed with the Microchip C30 compiler. The SBLXC32 supports the PIC32MX family of microcontrollers and was developed with the Microchip C32 compiler. These serial bootloaders enable the downloading of new firmware to the respective Microchip family of microcontrollers via the serial interface. The package includes the following:

  • Encrypted Serial Bootloader Source code for the respective compiler
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • PC XTEA Encryption Application binary image
  • PC XTEA Encryption Application source code (Visual C++ 2008 Express)
  • Encrypted Serial Bootloader User Manual

US $150 SBLXCCS18 - PIC18F Family Encrypted Serial bootloader
US $150 SBLXC30 - PIC24/dsPIC33 Family Encrypted Serial bootloader
US $150 SBLXC32 - PIC32MX Family Encrypted Serial bootloader


SD/MMC card Bootloaders for PIC Microcontrollers

Brush Electronics SD/MMC card Bootloaders for Microchip Microcontrollers supporting microSD, miniSD and standard SD form factors. These bootloaders enable the PIC firmware to ugraded via an SD/MMC card and is ideal for sending new images to end customers at remote sites to upgrade firmware. Upgrading the software is as simple as inserting/exchanging the SD/MMC card and power cycling the target system. We offer both standard and encrypted versions of SD/MMC bootloaders:
  • SD/MMC - SD/MMC card Bootloader for PIC18F series Microcontrollers
  • SD/MMC - SD/MMC card Bootloader for PIC24/dsPIC33 series Microcontrollers
  • SD/MMC - SD/MMC card Encrypted Bootloader for PIC24/dsPIC33 and PIC32 series Microcontrollers

SD/MMC Card Bootloader for PIC18F series Microcontrollers

The Brush Electronic's SD/MMC Bootloader - PIC18F Series has been developed to enable the firmware upgrade of SD/MMC card equipped Microchip PIC18F series microcontrollers. The bootloader will enable the upgrade of the user application firmware in the microcontroller and, optionally, the data in an external SPI based serial EEPROM.

The user manuals for the PIC18F and PIC24/dsPIC33 series SD/MMC bootloaders along with a demonstration image for the Explorer 16 development board configured with the PIC24FJ128GA010 PIC microcontroller and the Microchip SD/MMC PICTail board can be found here.

Bootloader source code versions are available for the CCS PIC18 and the Microchip C18 compilers.

US $100 SD/MMC Card Bootloader for PIC18F CCS Source Code
US $100 SD/MMC Card Bootloader for PIC18F C18 Source Code


SD/MMC Card Bootloader for PIC24/dsPIC33 series Microcontrollers

The Brush Electronic's SD/MMC Bootloader - PIC24/dsPIC33 Series has been developed to enable the firmware upgrade of SD/MMC card equipped Microchip PIC24/dsPIC33 series microcontrollers. The bootloader will enable the upgrade of the user application firmware in the microcontroller and, optionally, the data in an external SPI based serial EEPROM.

The user manuals for the PIC18F and PIC24/dsPIC33 series SD/MMC bootloaders along with a demonstration image for the Explorer 16 development board configured with the PIC24FJ128GA010 PIC microcontroller and the Microchip SD/MMC PICTail board can be found here.

The source code is available in two versions, the base version enabling the bootloading of the PIC and the extended version supporting bootloading of the PIC and an external SPI based EEPROM.

US $100 SD/MMC Card Bootloader for PIC24/dsPIC33 Source Code
US $175 SD/MMC Card Bootloader PIC24/dsPIC33 with XEE support


SD/MMC Card Encrypted Bootloader for PIC24/dsPIC33 and PIC32 series Microcontrollers

The Brush Electronic's SD/MMC Encrypted Bootloaders - have been developed to enable the firmware upgrade of SD/MMC card equipped Microchip PIC24/dsPIC33 or PIC32 series microcontrollers. The bootloader will enable the upgrade of the user application firmware in the microcontroller and the data in an external SPI based serial EEPROM.

The user manuals for the PIC18F, PIC24/dsPIC33 and PIC32MX series SD/MMC bootloaders along with a demonstration image for the Explorer 16 development board configured with the PIC24FJ128GA010 PIC microcontroller and the Microchip SD/MMC PICTail board can be found here. This image is for the unencrypted version of the bootloader.

US $250 SD/MMC Card Encrypted Bootloader PIC24/dsPIC33 with XEE support
US $250 SD/MMC Card Encrypted Bootloader PIC32 with XEE support


Ethernet Bootloaders for PIC Microcontrollers

Brush Electronics offers families of Ethernet Bootloaders for Microchip Microcontrollers:
  • ENC - PIC18F Ethernet Bootloader for Microchip ENC28J60 controller
  • RTL - PIC18F Ethernet Bootloader for Realtek RTL8019AS controller
  • EPIC - Ethernet Bootloader for Microchip PIC18FxxJ6x PICs with Embedded Ethernet
  • EPICX - PIC18F97J60 family Encrypted Ethernet Bootloader
  • EBLEX - PIC24/dsPIC33 and PIC32 Encrypted Ethernet Bootloaders for Microchip ENC28J60 controller
  • EBLE100X - PIC24/dsPIC33 and PIC32 Encrypted Ethernet Bootloaders for Microchip ENC424J600 / ENC624J600 controller
  • EBLP100X - PIC32MX795 family Encrypted Ethernet Bootloader


EBLPX - PIC18F97J60 family Encrypted Ethernet Bootloader

This Ethernet bootloader will enable the downloading of new firmware to the Microchip PIC18F97J60 family of microcontrollers via the embedded Ethernet controller. The package includes the following:

  • PIC Ethernet bootloader assembly source code
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • PC XTEA Encryption Application binary image
  • PC XTEA Encryption Application source code (Visual C++ 2008 Express)
  • Encrypted Ethernet Bootloader User Manual

US $100 PIC18F97J60 Family Encrypted Ethernet bootloader


PIC32MX795 Family Encrypted Ethernet bootloaders

This Ethernet bootloader will enable the downloading of new firmware to the Microchip PIC32MX795 family of microcontrollers via their embedded Ethernet controllers. The package includes the following:

  • PIC Ethernet bootloader source code for the C32 compiler
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • PC XTEA Encryption Application binary image
  • PC XTEA Encryption Application source code (Visual C++ 2008 Express)
  • Encrypted Ethernet Bootloader User Manual

US $200 PIC32MX795 Family 10/100Mbps Encrypted Ethernet bootloader


PIC24/dsPIC and PIC32MX Encrypted Ethernet bootloaders for ENC28J60 Ethernet Controller

These Ethernet bootloaders enable the downloading of new firmware to the Microchip microcontrollers via the Microchip ENC28J60 Ethernet controller. The package includes the following:

  • PIC Ethernet bootloader source code for the C30 or C32 compiler
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • PC XTEA Encryption Application binary image
  • PC XTEA Encryption Application source code (Visual C++ 2008 Express)
  • Encrypted Ethernet Bootloader User Manual
The source code has been preconfigured to support the Microchip Explorer16 with Ethernet PICTail. Modification to support other platforms is relatively straight forward. An optional customization service is available if you would rather have this customization performed for you.

US $100 PIC24/dsPIC33 Encrypted Ethernet bootloader for ENC28J60
US $150 PIC32MX Encrypted Ethernet bootloader for ENC28J60


PIC24/dsPIC33 and PIC32 Encrypted Ethernet bootloaders for ENC424J600/ENC624J600 Ethernet Controller

This Ethernet bootloader will enable the downloading of new firmware to the Microchip microcontrollers via the Microchip 10/100 ENC424J600/ENC624J600 Ethernet controllers. The package includes the following:

  • PIC Ethernet bootloader source code for the C30 or C32 compiler
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • PC XTEA Encryption Application binary image
  • PC XTEA Encryption Application source code (Visual C++ 2008 Express)
  • Encrypted Ethernet Bootloader User Manual

US $150 PIC24/dsPIC33 10/100Mbps Encrypted Ethernet bootloader
US $200 PIC32 10/100Mbps Encrypted Ethernet bootloader


PIC18F Ethernet Bootloader Source Code for ENC28J60 Ethernet Controller

This Ethernet bootloader will enable the downloading of new firmware to the Microchip PIC18F series microcontrollers via the Microchip ENC28J60 Ethernet controller. This Bootloader does NOT support the J series microcontrollers. Processors currently supported include the PIC18F 252/452/452/2520/2525/2620/2685/4620/4629/4685/6527/6720/8621/8722. Porting code to other variants of the PIC18F processors listed is straight forward. The package includes the following:

The source code has been preconfigured to support a number of target hardware platforms including the Brush Electronics' PIC18F2620 and PIC18F4620 reference designs, the Microchip PICDEMTM HPC, the CCS PICENS, the LJCV Electronic's PICNET1 and eIP-10 boards, and the EDTP Frame Thrower+ and EDTP Frame Thrower II boards. Modification to support other platforms is relatively straight forward. An optional customization service is available if you would rather have this customization performed for you.

US $50 PIC18F Ethernet bootloader for ENC28J60 Source Code


Ethernet Bootloader Source Code for Realtek Ethernet Controller

This Ethernet bootloader will enable the downloading of new firmware to the Microchip PIC18F 252/452/4620/6621/6627/6722/8722 Microcontrollers via the Realtek RTL8019AS Ethernet controller. Porting code to other variants of the PIC18F processors listed is straight forward. The package includes the following:

  • PIC Ethernet bootloader assembler source code and MPLAB project files
  • PC Bootloader Application binary image
  • PC Bootloader Application source code (Delphi / FreePascal)
  • Ethernet Bootloader User Manual
The source code has been preconfigured to support the Microchip PICDEM.NETTM Ethernet Development Board, the CCS Internet Board, and the Modtronix SBC65EC. Modification to support other platforms is relatively straight forward. An optional customization service is available if you would rather have this customization performed for you.

US $50 PIC18F Ethernet bootloader for RTL8019AS Source Code

Ethernet Bootloader for PIC18F97J60 Family of PICs with Embedded Ethernet Controllers

This Ethernet bootloader will enable the downloading of new firmware to the Microchip PIC18F97J60 Family of microcontrollers via the PIC's embedded Ethernet controller.

Ethernet Bootloader Images for the PIC18F97J60 family are NOT available for free. A low cost NON COMMERCIAL use Ethernet Bootloader image license for members of the PIC18F97J60 family is available. The image license includes images for:

  • Brush Electronics' PIC18F97J60 Ethernet Development Board reference design
  • Microchip PICDEM.NET2 Ethernet Development Board
  • EDTP Electronics Ethernet Mini board
  • Generic images for each of these PIC18FxxJ6x family members
Images for other hardware platforms are available via our image customization service.

The Ethernet Bootloader package includes the following:

The source code has been preconfigured to support the Brush Electronics' PIC18F97J60 Ethernet Development Board reference design and the Microchip PICDEM.NET2 Ethernet Development Board and the EDTP Electronics Ethernet Mini board. Modification to support other platforms is relatively straight forward. An optional customization service is available if you would rather have this customization performed for you.

US $20 NON COMMERCIAL USE - PIC18F97J60 family Ethernet Bootloader Software Image License
US $80 PIC18F97J60 family Ethernet Bootloader Source Code


Ethernet Bootloader Images

These Bootloader Images have been compiled for a range of reference platforms. These software images are free for NON COMMERCIAL use. An optional customization service is available to adapt the software to a different hardware platform or PIC18F Microcontroller.

This Ethernet bootloader will enable the downloading of new firmware to the Microchip microcontroller. The package available here includes the bootloader image for the microcontroller, the PC programming application and a sample program, based on Brush Electronics' UDP Network Proof-of-Concept application, for exercising the bootloader and testing the target platform.

  • PIC Ethernet bootloader image file
  • PC Bootloader Application binary image
  • Ethernet Bootloader User Manual
  • Sample program, based on Brush Electronics' UDP Network Proof-of-Concept application, for exercising the bootloader and testing the target platform (not available for all platforms).
Platforms currently supported:
  • Brush Electronics PIC18F2620 - ENC28J60 Reference Hardware Design
  • Brush Electronics PIC18F4620 - ENC28J60 Reference Hardware Design
  • CCS PICENS Ethernet Development Board
  • Celeritous PICWEB1 PIC18F67J60 Embedded Web Server
  • EDTP Frame Thrower+
  • EDTP Frame Thrower II
  • LJCV Electronics eIP-10 and PICNET1 development boards
  • Microchip PICDEM TM HPC with PICTail or EDTP Frame Thrower
  • Microchip PICDEM.NET TM with RealTek RTL8019AS Ethernet Controller
  • Olimex PICWEB development board


Sensirion SHT Software driver for SHT family of temperature/humidity sensors

A software driver, developed in C for the Sensirion SHT sensors, is available for the Microchip PIC series microcontrollers. The driver was developed to support our Environmental monitoring systems. The driver includes the low level communications interface including CRC checksum validation of the sensor datastream, temperature compensation of the humidity sensor, dew point calculation and temperature and humidity scaling. Driver versions are available for the CCS PIC18 and the Microchip C18 compilers.

US $50 Sensirion SHT Driver CCS Compiler Source Code
US $50 Sensirion SHT Driver C18 Compiler Source Code


SD/MMC Card driver and test utilities

Low level SPI drivers and utilities for interfacing SD, MMC and SDHC cards to PIC Microcontrollers. This software is supplied along with an application that incorporates low level SD/MMC drivers and is intended to provide a working example of the driver. With the supplied application you can perform low level read and write operations to the SD/SDHC/MMC card. A user command line interface (CLI) is provided via the serial port.

CLI supports the following commands:

  • EXPLORE
  • INIT
  • QFORMAT
  • RESET
  • SECTOR
EXPLORE: this command enables you to quickly example the data structure on a disk such as the location and contents of the Master Boot Record (MBR), the partition table (if present), the boot sector, the location and view of the first sector of FAT and the directory. Sectors are displayed as a standard hex dump with both HEX and ASCII representations.

INIT: initialize the SD/SDHC/MMC interface.

QFORMAT: Performs a quick format of the SD/SDHC/MMC card by clearing the FATs and the Root Directory. It uses the directory structure information on the media.

RESET: Resets the PIC

SECTOR : Displays sector xxx. The space bar advances thru subsequent sectors.

The utilities include the inspection of the masterboot record, bootsector, directory structure and FAT if present. The utilities will enable sectors to be examined with both HEX and ASCII representation. The utilities include a quick format function for reinitializing the existing file system on the media.

The driver is currently available for the PIC24/dsPIC33 series microcontrollers with the in Microchip C30 compiler, and the PIC18F series microcontollers with the C18 and CCS C Compiler versions however the code can be readily ported to other compilers.

For information on how to implement an SD/MMC card interface on a PIC microcontroller, refer to our hardware reference designs located on our projects page.

Licenses for integration of SD Cards or MMC Cards into products may be required from Microsoft, IBM, the SD Card Association (for SD Cards) and the Multimedia Association (for MMC Cards).

US $40 SD/MMC Driver & Utilities Source Code for PIC18F with CCS
US $40 SD/MMC Driver & Utilities Source Code for C18
US $40 SD/MMC Driver & Utilities Source Code for C30


Software driver for SD/MMC Card File System for Microchip Microcontrollers

This is an SD/SDHC/MMC software driver for Microchip microcontrollers enabling the microcontroller to read and write the SD/SDHC/MMC cards using a File system. This driver supports the standard 8.3 filename convention used by DOS. SD/MMC cards written by this driver can be read by a PC and likewise the driver can read files written by a PC. The user manual is available HERE.

This code is an implementation of the ELM Generic File System module which has been ported to the Microchip PIC32MX series microcontroller with the Microchip C32 compiler, the Microchip PIC24/dsPIC33 series microcontrollers with the CCS PCD and Microchip C30 compilers and the PIC18F series Microcontrollers with the CCS PCH and Microchip C18 Compilers. The drivers for the PIC18 and PIC24/dsPIC33 has been extensively debugged and modified.

For the PIC18F series microcontrollers, the driver is supplied as a hybrid Data Logger application which also features a DOS like command line interface which incorporates a software real time clock (required for the file system). The data logger application, based on a real logger, was designed to record 12 bytes of data every 50ms and was tested successfully at 12 bytes per 10ms however the actual performance depends on many factors such as CPU speed, memory card access speed and other tasks being handled by the PIC. The data logger application demonstrates the concept of caching the incoming raw data while SD/MMC write operations of the data are in effect. Note that this is a proof of concept application. The marriage of the data logger function and the DOS command line interface are intended to show the developer how to use the various functions. The file system drivers support standard (high performance) and newly added LITE configuration modes. The standard mode implements a separate 512 byte read/write buffer for the file system and for each file. The LITE mode, enabled via a #define directive in the source code, offers all the features of the standard mode and is well suited to applications and controllers that have limited RAM available. The LITE mode shares a single 512 byte read/write buffer between the file system and all open files and is capable of supporting hundreds of files open concurrently. For high performance applications that require two or more files open concurrently, the standard mode is recommended 

     RAM requirements:         Standard           Lite
     File System overhead        560              560
     Per File Overhead           540               38
    Subset of file specific functions:
    FRESULT f_open (FIL *fp, char *path, BYTE mode); // Open or create a file
    FRESULT f_read (FIL *fp, void *buff, WORD btr, WORD *br); // Read from a file
    FRESULT f_close (FIL *fp); // Close a file
    FRESULT f_lseek (FIL *fp, DWORD ofs); // Seek file pointer
    FRESULT f_opendir (DIR *scan, char *path); // Initialize to read a directory
    FRESULT f_readdir (DIR *scan, FILINFO *finfo); // Read a directory item
    FRESULT f_stat (char *path, FILINFO *finfo); // Get file status
    FRESULT f_getfree (DWORD *nclust); // Get number of free clusters
    FRESULT f_mountdrv (void); // Force initialize the file system
    void f_get_error_mesg(FRESULT Mesg, char *destination); // Convert the FRESULT return code to a string
    FRESULT f_write (FIL *fp, void *buff, WORD btw, WORD *bw); // Write file
    FRESULT f_sync (FIL *fp); // Flush cached information of a writing file
    FRESULT f_unlink (char *path); // Delete a file or directory
    FRESULT f_mkdir (char *path); // Create a directory
    FRESULT f_chmod (char *path, BYTE value, BYTE mask); // Change file attriburte
    FRESULT f_rename ( char *path_old, char *path_new); // Rename a file / directory

For the PIC24/dsPIC33 series microcontrollers, the driver is supplied with a sample application which features a DOS like command line interface.

    CLI commands:
    COPY src dst - copy file 'scr' to 'dst'
    CREATE name - create the file 'name'
    DATE [dd/mm/yy] - set / display time
    DELETE name - delete the file 'name'
    DIR - list directory
    DUMP name - hex dump file 'name'
    EXPLORE - explores the SD card data structure
    INIT - initialise the SD card file system data structures
    LOG [START|STOP] - display / change logging status
    MD name - create directory 'name'
    RESET - reset the PIC Microcontroller
    STATUS - display system status
    TIME - set / display time
    TYPE name - list contents of text file 'name'

For the PIC32MX series microncontrollers, the driver is supplied with a sample application however this application does NOT include the DOS like command line interface. HOWEVER the PIC32MX version comes bundled with the PIC24/dsPIC33 driver and sample application that does feature the DOS like command line interface.

The driver includes the low level SD/MMC SPI drivers, the low level disk I/O drives, file level operations, and a DOS like user interface. For information on how to implement an SD/MMC card interface on a PIC microcontroller, refer to our hardware reference designs located on our projects page.

Aside for hardware and software challenges, the integration of SD and MMC cards in embedded systems is not without it headaches. Licenses for integration of SD Cards or MMC Cards into products may be required from Microsoft, IBM, the SD Card Association (for SD Cards) and the Multimedia Association (for MMC Cards).

Microsoft has been granted patents covering the File Allocation Table (FAT) file system. These patents pertain to the integration of long file names with legacy DOS file names in the same data structure. In order to avoid infringing on Microsoft's patents in this area, our software does not support long file names nor does it support formatting the media. IBM holds patents pertaining to extended file system attributes. Our code does not support extended file attributes.

It is up to the purchaser of this software to ascertain for themselves if licenses are required from any or all of these or other organizations for the integration of the media or our software into their products. In the event licenses are required from any of these or other organization, it is up to the purchaser of this software to acquire, at their own cost, such licenses directly from the license holders.

US $75 SD/MMC File System Source Code for CCS PIC18F
US $140 SD/MMC File System Source Code for CCS PIC18/PIC24/dsPIC33
US $75 SD/MMC File System Source Code for C18
US $75 SD/MMC File System Source Code for C30
US $140 SD/MMC File System Source Code for C30 and C32


How to implement an SD/MMC Card with a PIC Microcontroller

A number of hardware reference designs incorporating SD/MMC Cards are available on our Projects page.

For a 3.3volt PIC system, the minimum interface between an SD/MMC card and the PIC is four I/O lines which include the three SPI bus lines (SCK, SDO and SDI) the fourth line is the chip select. Optionally two additional lines connect to the SD/MMC socket for Card Detect (CD) and Write Protect (WP). For 5 volt PICs, level translation is required between the 5 volt I/O of the PIC and the 3.3 volt I/O of the SD/MMC Card. Level translation for the PIC SDO, SCK and CS outputs can be implemented with simple resistor voltage dividers. Coming from DO of the SD/MMC Card to the SDI input of the PIC is not so straight forward and requires a TTL buffer. This is because the PIC, in SPI mode, has the SDI input configured as a Schmidt trigger input and the guaranteed logic high out of the SD/MMC card is less than the guaranteed logic high level of the PIC.

When selecting a PIC for applications that write to a media card, there are two main criteria; there is sufficient RAM to support the access method and the PIC supports an SPI bus. SD/MMC Cards must be written in 512 byte blocks. This is also the sector size of the SD/MMC card. So for example, to append a byte to a file, the sector must be read into a buffer, the location modified, and the sector written back to disk.

If using the Brush Electronics' file system driver in standard mode (high performance), a 512 byte sector buffer is required for file system management and one 512 byte buffer is required for each open file. This means a PIC with 1500 bytes of RAM, such as the PIC18F452, when using the standard file system configuration mode, can realistically have only a single file open at a time. The PIC18F4620, which is pin compatible with the PIC18F452 has 3900 bytes of ram available and therefore can have multiple files open simultaneously.

When the file system driver is configured for LITE mode, a single sector buffer is shared by the file system and all open files. This means a PIC with 1500 bytes of memory, such as the PIC18F452, can have multiple files open simultaneously. The LITE configuration mode is not recommended for high performance applications that require access to multiple open files.

SD/MMC Card integration troubleshooting guidelines can be found here.