Document No.: FT_000061
FT2232H DUAL HIGH SPEED USB TO MULTIPURPOSE UART/FIFO IC
Version 2.21
Clearance No.: FTDI#77
4.8.1 Outgoing Fast Serial Data
To send fast serial data out of the FT2232H, the external device must drive the FSCLK clock. If the
FT2232H has data ready to send, it will drive FSDO output low to indicate the start bit. It will not do this
if it is currently receiving data from the external device. This is illustrated in Figure 4.14.
FSCLK
0
Start
Bit
D0
D1
D2
D3
D4
D5
D6
D7
SRCE
Source
Bit
FSDO
Data Bits - LSB first
Figure 4.14 Fast Opto-Isolated Serial Interface Output Data
Notes :-
1. The first bit output (Start bit) is always 0.
2. FSDO is always sent LSB first.
3. The last serial bit output is the source bit (SRCE). It indicates which channel the data has come
from. A „0‟ means that it has come from Channel A, a „1‟ means that it has come from Channel B.
4. If the target device is unable to accept the data when it detects the START bit, it should stop the
FSCLK until it can accept the data.
4.8.2 Incoming Fast Serial Data
An external device is allowed to send data into the FT2232H if FSCTS is high. On receipt of a zero START
bit on FSDI, the FT2232H will drop FSCTS on the next positive clock edge. The data from bits 0 to 7 are
then clocked in (LSB first). The last bit (DEST) determines where the data will be written to. The data can
be sent to either channel A or to channel B. If DEST= „0‟, the data is sent to channel A, (assuming
channel A is enabled for fast serial mode, otherwise the data is sent to channel B). If DEST= „1‟ the data
is sent to channel B, (assuming channel B is enabled for fast serial mode, otherwise the data will go to
channel A. (Either channel A, channel B or both channels must be enabled as fast serial mode or the
function is disabled). This is illustrated in Figure 4.15.
FSCTS
FSCLK
0
D0
D1
D2
D3
D4
D5
D6
D7
DEST
FSDI
Start
Bit
Destination
Bit
Data Bits - LSB first
Figure 4.15 Fast Opto-Isolated Serial Interface Input Data
Notes :-
1. The first bit input (Start bit) is always 0.
2. FSDI is always received LSB first.
3. The last received serial bit is the destination bit (DEST).It indicates which channel the data should
go to. A „0‟ means that it should go to channel A, a „1‟ means that it should go to channel B.
4. The target device should ensure that CTS is high before it sends data. CTS goes low after data bit
0 (D0) and stays low until the chip can accept more data.
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