SD Loader

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Introduction

Legacy computer systems typically load and save programs over serial ports. This is often done by attaching a PC and running a terminal program to send/receive programs to the legacy systems. Integrating modern storage, like SD cards, can be a serious challenge into legacy designs.

Replacing the external PC offers the opportunity to more easily transport the system. A compact solution that emulates the PC for transfers would be useful.

This design transfers files to/from an SD card via a serial port. It runs a menu driven program on small OLED to control transfers and supports SD cards up to 32GB (FAT32 formatted). The serial interface has RTS/CTS hardware handshake support. It can run with 5V or 3.3V target systems or at RS-232 levels. Custom cards could easily be added to emulate cassette interfaces or run.

Features

  • Supports SD cards up to 32GB
    • FAT32 formatted
  • Serial interface
    • Full hardware Handshake support

Cards

QT Py Breakout Card

QT Py Breakout P18212-720px.jpg

  • Power via USB C cable

QTPy49 Card

QTPy49 FRONT REV1.png

SD CARD X49

SD CARD X49 BW.PNG

MyMenu

MyMenu-X3-AssySheet.PNG

RS-232 Level Shifter (Optional)

DTE P562-720px.jpg

Level Shifter (Optional)

LVL SH P18228-720px.jpg

QT Py Breakout Card (on GRID49 card) Cabling

  • QT Py uses (2) 1x7 male headers for signals
    • Cut off 1 set of holes of (2) female housings to make 1x7 female headers
  • SD Card uses (1) 1x8 header
  • MyMenu uses (1) 1x5 header
  • QT Py uses 2x8 header for 3.3V and Ground
    • Use 2x3 female housings
  • 40mm cables to Host Target

QT Py Breakout Card to MyMenu Cabling

QT Py SIGNAL MyMenu COLOR
1 (A0) INT(D6) P2-5 GRY
5 (SDA) SDA P2-3 WHT
6 (SCL) SCL P2-4 BRN
GND GND P2-1 BLK
VCC +3.3V P2-2 RED

QT Py Breakout Card to SD_CARD_X49 Cabling

QT Py SIGNAL SD_CARD_X49 COLOR
03 (A3) SS* J1-5 GRY
09 (SCK) SCK J1-3 BLU
10 (MI) MISO J1-2 BRN
11 (MO) MOSI J1-4 WHT
GND GND J1-1 BLK
VCC 3.3V J1-8 RED

QT Py Breakout Card to Host Serial

QT Py SIGNAL COLOR
GND GND BLK
7 (TX) TX WHT
8 (RX) RX BRN
2 (A1) RTS* GRY
3 (A2) CTS* ORA

QTPy49 Card Cabling

QTPy49 CAD.PNG

  • QT Py Card has function specific headers

QTPy49 Card to MyMenu Cabling

QTPy49 SIGNAL MyMenu COLOR
J5-1 GND P2-1 BLK
J5-2 +3.3V P2-2 RED
J5-3 SDA P2-3 WHT
J5-4 SCL P2-4 BRN
J9-3 INT(AD0) P2-5 GRY

QTPy49 Card to SD_CARD_X49 Cabling

QT Py SIGNAL SD_CARD_X49 COLOR
J3-1 GND J1-1 BLK
J3-2 3.3V J1-8 RED
J3-4 (MO) MOSI J1-4 WHT
J3-5 (MI) MISO J1-2 BRN
J3-6 (SCK) SCK J1-3 BLU
J6-3 (A3) SS* J1-5 GRY

QTPy49 Card to Host Serial

QTPy49 SIGNAL COLOR
J8-3 (AD1) RTS* GRY
J7-1 (AD2) CTS* ORA
J4-4 (RX) RX BRN
J4-3 (TX) TX WHT
J4-2 (VCC) +3.3V Xlator (only)
J4-1 (GND) GND BLK

Software

  • Developed using Arduino IDE V1.8.xx
  • Arduino IDE Setup for QT Py
  • Requires Arduino IDE version 1.8 or higher
  • Add to Preferences Additional Boards Manager URLs
https://adafruit.github.io/arduino-board-index/package_adafruit_index.json
 

pinMode(pin, INPUT_PULLUP)

#if defined(ARDUINO_SAMD_ZERO) && defined(SERIAL_PORT_USBVIRTUAL)
  // Required for Serial on Zero based boards
  #define Serial SERIAL_PORT_USBVIRTUAL
#endif

const char str[] = "My very long string";

Human Interface Design (HID)

SD Card

  • Library
  • Example files

SD Card Library

  • SD Card library
    • The SD library allows for reading from and writing to SD cards, e.g. on the Arduino Ethernet Shield
    • Based on sdfatlib
    • The library supports FAT16 and FAT32 file systems on standard SD cards and SDHC cards
    • It uses short 8.3 names for files
    • The file names passed to the SD library functions can include paths separated by forward-slashes, /, e.g. “directory/filename.txt”
    • Because the working directory is always the root of the SD card, a name refers to the same file whether or not it includes a leading slash (e.g. “/file.txt” is equivalent to “file.txt”)
    • As of version 1.0, the library supports opening multiple files.
    • The communication between the microcontroller and the SD card uses SPI, which takes place on digital pins 11, 12, and 13 (on most Arduino boards) or 50, 51, and 52 (Arduino Mega)
    • Additionally, another pin must be used to select the SD card
    • This can be the hardware SS pin - pin 10 (on most Arduino boards) or pin 53 (on the Mega) - or another pin specified in the call to SD.begin()

SD Card Example Code

SD Card Connections

 ** SCLK - CLK - pin 13
 ** MISO - SDI - pin 12
 ** MOSI - SDO - pin 11
 ** SS - CS - depends on your SD card shield or module.

Serial

  • Serial Reference
  • Serial.begin(speed)
  • Serial.available()
    • Get the number of bytes (characters) available for reading from the serial port.
    • This is data that’s already arrived and stored in the serial receive buffer (which holds 64 bytes).
    • Turn off/on receive handshake based on Serial.available() count and storage
  • Serial.write()
    • Writes binary data to the serial port
    • This data is sent as a byte or series of bytes
    • To send the characters representing the digits of a number use the print() function instead.
    • Syntax
Serial.write(val)
Serial.write(str)
Serial.write(buf, len)

References

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