NanoBoard 3000 - SD Card Reader (User FPGA)
The Secure Digital (SD) memory card is among a host of such cards available in today's world of storage-hungry devices, such as PDAs and digital cameras. The NanoBoard 3000 provides a reader for this type of memory card – dedicated for use by the User FPGA – by way of a KSDC012551 connector, from Konvee.
Secure Digital (SD) memory card reader for use in
an FPGA design.
The connector features a push-in/push-out ejection mechanism, locking the SD card firmly in place. The card is inserted face down.
The connector provides Card Detection and Write Protection switches, to flag whether a card has been inserted, and the write status of that card. Both switches are commoned to the motherboard's GND and are normally open (i.e. when no card is inserted). When a card is inserted:
- The Card Detection switch will close.
- The Write Protection switch will close only if the SD card is enabled for writing to. If the card's write protect tab is in the 'Locked' position (typically down) the card is Read Only and the Write Protection switch will remain open.
Single inverter gate devices are used on the output lines from these switches (SN74LVC1G04, from Texas Instruments). While the switches are open, 4K7 pull-up resistors connected to the board's 3.3V power supply ensure logical '0' is sent to the User FPGA on corresponding signal lines SD_DETECT and SD_PROTECT, respectively. Switch closure will result in a logical '1' being sent.
All I/O signals relating to the SD card are made available to the User FPGA. Although SD cards support three modes of data transfer – SD (1-bit), SD (4-bit) and SPI – only the 4-wire SPI mode is readily supported through use of an intermediate SD Card Controller. This peripheral is placed in the FPGA design and sits between a processor in the design and the SD card reader on the motherboard.
Table 1 summarizes the pinout of an SD card and the signals made available to the User FPGA. The table highlights in grey those signals that relate to use of the card in the SPI mode of data transfer.
Table 1. Use of SD card signals.| Pin | Signal Function in SD mode | Signal Function in SPI mode | Signal arriving at User FPGA... |
|---|---|---|---|
| 1 | Data Line 3 | Chip Select | SD_DAT3 |
| 2 | Command Line | Master Out | SD_CMD |
| 3 | Ground | Ground | - |
| 4 | Voltage Supply | Voltage Supply | - |
| 5 | Clock | Clock | SD_CLK |
| 6 | Ground | Ground | - |
| 7 | Data Line 0 | Master In | SD_DAT0 |
| 8 | Data Line 1 | Unused | SD_DAT1 |
| 9 | Data Line 2 | Unused | SD_DAT2 |
Should you wish to use the SD card's 1-bit SD mode, where data is transferred over the SD_DAT0 line, you will need to create your own SD Controller, which would reside in the FPGA design. The same applies to use of the card's 4-bit SD mode, where data is transferred in parallel over all four data lines.
Location on Board
The SD card reader (designated J30) is located along the bottom edge on the solder side of the board. Looking from the front, it can be found between the USB ports.
SD Card reader (as seen from the front of the board).
The two inverter gate devices (designated U67 and U68) are located to the right of the SD card reader (J29) used for the NanoTalk Controller.
Schematic Reference
The SD card reader circuitry can be found on Sheet 48 (CON_SD_KSDC012551.SchDoc, entitled SD-Card) of the motherboard schematics.
Design Interface Component
Table 2 summarizes the available design interface component that can be placed from the FPGA NB3000 Port-Plugin.IntLib for access to, and communications with, an SD memory card.
| Component Symbol | Component Name | Description |
|---|---|---|
| SD_CARD | Place this component to interface to the Secure Digital (SD) card reader and write/read an SD memory card inserted within. |
The following signals, although not part of the port component, are made available to the User FPGA:
SD_DAT1
SD_DAT2
To access these signals and use them in a design, you will need to place ports appropriately mapped to the device pins on which these signals arrive.
Further Device Information
For more information on the KSDC012551 connector, refer to the datasheet (KSDC012551.pdf) available at www.konvee.com.
For more information on the single inverter gate device, refer to the datasheet (sn74lvc1g04.pdf) available at www.ti.com.