DCSD Cable

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Annotated photo of the main DCSD PCB

The DCSD Alex cable is used in factories to communicate over serial to run tests and write to the SysCfg (for serial definitions, etc) during production. These cables are produced by ShenZhen Alex Connector Co., Ltd. in China. They can be purchased from obscure markets. There are two known types of DCSD cable. An older one, with lights and only one USB female USB connector, and a newer model, which lacks lights, and has two female USB connectors.

PCB

Top of the board

Label Chip Datasheet Notes
D1 Low Power Consumption Voltage Regulator with ON/OFF Switch http://www.s-manuals.com/pdf/datasheet/x/c/xc6215_series_torex.pdf
D5
D6 Tied to TX and an input voltage of 3.3V on the UART J5 pads, this may be a protection in case the host shorts?
U1 Micrel 2026A Dual-Channel Power Distribution Switch https://web.archive.org/web/20141010122122/http://www.xilinx.com/products/boards/ml510/datasheets/mic2076-2bm.pdf
U2
U3 FTDI FT232RQ UART IC http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf Handles stoplight LED controls
U4 Micrel MIC5219 http://datasheet.datasheetarchive.com/originals/library/Datasheets-EDS7/DSAEDA000124178.pdf 500mA Peak Output LDO Regulator
U5 FTDI FT232RQ UART IC http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf Handles serial mux interface from iPhone
U6 SMSC USB2514 4-port USB hub http://www.mouser.com/catalog/specsheets/2514.pdf
  • The use of this deprecates the previous "Y" style cable, which used two separate USB cables for serial and iPhone data communication
  • Three ports are used:
    1. iPhone Data USB
    2. U4 FTDI IC
    3. U5 FTDI IC
U7 Microchip 24AA04/24LC04B http://ww1.microchip.com/downloads/en/DeviceDoc/21708G.pdf I2C Serial EEPROM (TSSOP Package)
X1 MKC 24 MHz Oscillator N/A I'm not 100% sure about the value of the chip, but this should be correct

Back of the board

Label Notes
J9 I believe these are used to flash the U7 EEPROM with USB IDs for use by the SMSC USB Hub, I have yet to dump the contents of the EEPROM to find out for sure.
J10
J11
J12

Other notes

  • The Lightning Connector has a specific Accessory ID flashed to it for enabling serial via the Tristar chip.
  • This PCB is quite easy to replicate, but without the proper Accessory ID you will need to mimic the protocol similar to how key2fr did in his research.
  • In theory, you can use the Tristar for JTAG through a similar board, but JTAG gets disabled by the device during boot due to production fusing status.

Uses

Verbose Boot

One use of the cable was to view verbose boot. You could access this by setting debug uarts in iRecovery or nvram, however, since iOS 9, this output has been obfuscated.

Shell over serial

Using qwertyoruiopz's serialsh, it is possible to get shell over serial. This is useful, because it does not require any additional daemons other than those shipped with iOS. An example use case for this would be protecting against bootloops.

Debugging the kernel

Using the DCSD cable, it is possible to attach GDB to the iOS kernel, and pause it's running.