FT201X Datasheet, PDF (30/49 Pages) List of Unclassifed Manufacturers – Future Technology Devices International Ltd.

FT201X USB I2C SLAVE IC Datasheet
Version 1.3
Document No.: FT_000627 Clearance No.: FTDI# 264
D2xx and VCP Interface under Windows
In Windows systems, the VCP driver is actually an additional layer on top of the D2xx driver. The D2xx
driver is always loaded and the VCP later may or may not be loaded on top of it, depending on the
requirements of the application.
When VCP is disabled, the device will appear only under Universal Serial Bus Controllers in the Device
Manager and no COM port is exposed. When the VCP is enabled, the device will appear under both the
Universal Serial Bus Controllers and the Ports (COM & LPT) sections in Device Manager.
The VCP interface will be disabled by default in the FT200XD and FT201X but can be enabled in one of
the following ways:
- An option bit in the MTP memory on the chip is checked each time that the device is enumerated,
and can cause the host computer to load the VCP layer. This allows each individual hardware unit
to enable or disable VCP as per it’s requirements. The MTP information in section 10 has further
details. FT_Prog can also be used to modify the MTP settings.
- The user may open the Properties for the device under Universal Serial Bus Controllers in Device
Manager in Windows and tick a box to load the VCP. Re-enumeration of the FT-X is necessary to
enable the new setting.
- By editing the driver FtdiBus.inf file (please refer to AN_107 below). Note that the FT_INF utility
available from the FTDI website can be used to help create the modifed inf files.
http://www.ftdichip.com/Support/Documents/AppNotes/AN_107_AdvancedDriverOptions_AN_00
0073.pdf
In other Operating systems (e.g. Linux, Mac and Windows CE), there are separate drivers for D2xx and
VCP, and only one of these drivers may be installed at any time. Therfore, the mode is selected by
installing the associated driver instead and the selection defined in the bullet points above has no effect.
9.1.2 Reading and Writing Data
Data from FT-X to the Host
When data is to be sent from the host computer to the external I²C master, the software application
writes this data to the FTDI driver using VCP or D2xx and this data is sent by the driver over USB to the
buffer in the device.
The external I²C master device may then perform an I²C read (Master receiver, Slave transmitter)
operation to retrieve the data.
The external I²C master should check if data is available to ensure that the data which has been read is
valid. The methods for this are described in section 9.2.2 below.
Data from Host to the FT-X
When data is to be sent from the external I²C master to the host computer, the external master performs
an I²C write (Master transmitter, Slave receiver) operation to the FT-X.
The FT-X stores this in its buffer and the data is sent back to the driver on the host computer over USB.
As with other FTDI devices, this happens when either the buffer in the device fills or when the latency
timer rolls over (so that partially filled buffers do not wait indefinitely), whichever happens first.
Note that when writing data to the FT-X over I²C, the external master should check whether there is
space available in the buffer inside the FT-X. It can do this using the methods shown in section 9.2.2
below.
The host computer application can then read the data from the driver buffer using the VCP interface or
the D2xx commands. In the case of D2xx, the number of bytes available may be determined using the
FT_GetQueueStatus command before doing the FT_Read.
Copyright © 2013 Future Technology Devices International Limited
30