DS_FT311D USB ANDROID HOST IC Datasheet
Version 1.2
Document No.: FT_000660 Clearance No.: FTDI# 305
5.2.1 UART Mode Signal Descriptions
The UART signals are fixed on the I/O pins. Table 5.1 UART Interface, details the pins for each of the
UART signals.
Pin No
Name
Type
Description
23
24
25
uart_txd
Output
Transmit asynchronous data output
uart_rxd
Input
Receive asynchronous data input
uart_rts#
Output
Request to send control output
Clear to send control input
uart_cts#
Input
26
29
Transmit enable (typically used for
RS485 designs)
uart_tx_active
output
Table 5.1 UART Interface
Note:
The FT311D has to enumerate the Android device before receiving data from the UART device.
This can be implemented by disconnecting the UART TXD signal of external UART device connected to the
FT311D uart_rxd signal until after the FT311D has established the USB link with Android device.
The connection sequence should be:
1. Connect FT311D to Android and complete enumeration.
2. Connect the TXD of UART device to FT311D’s RXD then start to receive data.
There are two methods to implement this function:
1.When FT311D connects to the Android device and enumeration is completed, the USB_ERROR# will
become Logic 0 (default Logic 1). This signal can be used to control the TTL gate (74LVC2G241,
74LVC1G125 or others) ON/OFF such that the TXD/RXD lines are connected/disconnected.
Figure 5-3 UART RXD and TXD connection gated by Enumeration
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