Copyright © 2013 Future Technology Devices International Limited

10

DS_FT312D USB ANDROID HOST IC Datasheet

Version 1.1

Document No.: FT_000816 Clearance No.: FTDI# 331

5 UART Interface

The interface implements a standard asynchronous serial UART port with flow control, for example

RS232/422/485. The UART can support baud rates from 300 to 921600 with RTS/CTS flow control. The

UART can support baud rates from 300 to 115200 with no flow control.

Data transfer uses NRZ (Non-Return to Zero) data format consisting of 1 start bit, 7 or 8 data bits, an

optional parity bit, and one or two stop bits. When transmitting the data bits, the least significant bit is

transmitted first. Transmit and receive waveforms are illustrated in Figure 5-1 and Figure 5-2:

Figure 5-1 UART Receive Waveform

Figure 5-2 UART Transmit Waveform

Baud rate (default =9600 baud), flow control settings (default = None), number of data bits (default=8),

parity (default is no parity) and number of stop bits (default=1) are all configurable from the Android

application. Please refer to ftdichip document number FT_000532 for further details.

http://www.ftdichip.com

TX_ACTIVE is transmit enable, this output may be used in RS485 designs to enable the line driver for

transmit mode.

UART RX buffer size is 5512 bytes and UART TX buffer size is 256 bytes.

Note: UART software flow control with XON/XOFF is not supported

UART hardware flow control with DTR/DSR is not supported

Note:

The FT312D 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

FT312D RXD signal until after the FT312D has established the USB link with Android device.

The connection sequence should be:

1. Connect FT312D to Android and complete enumeration.

2. Connect the TXD of UART device to FT312D’s RXD then start to receive data.

There are two methods to implement this function:

1.When FT312D 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.