Document No.: FT_000061
FT2232H DUAL HIGH SPEED USB TO MULTIPURPOSE UART/FIFO IC
Datasheet Version 2.09
Clearance No.: FTDI#77
4.8 Fast Opto-Isolated Serial Interface Mode Description
Fast Opto-Isolated Serial Interface Mode provides a method of communicating with an external device
over USB using 4 wires that can have opto-isolators in their path, thus providing galvanic isolation
between systems. If either channel A or channel B is enabled in Fast Opto-Isolated Serial mode then the
pins on channel B are switched to the fast serial interface configuration. The I/O interface for fast serial
mode is always on channel B, even if both channels are being used in this mode. An address bit is used
to determine the source or destination channel of the data. It therefore makes sense to always use at
least channel B or both for fast serial mode, but not A own its own.
Fast serial mode is enabled by setting the appropriate bits in the external EEPROM. The fast serial mode
can be held in reset by setting a bit value of 10 using the Set Bit Bang Mode command. While this bit is
set the device is held reset – data can be sent to the device, but it will not be sent out by the device until
the device is enabled again. This is done by sending a bit value of 0 using the set bit mode command.
See application note AN2232L-02, “Bit Mode Functions for the FT2232D” for more details and
examples.
When either Channel B or both Channel A and B are configured in Fast Opto-Isolated Serial Interface
mode the IO timing of the signals used are shown in Figure 4.13 and the timings are shown in Table
4.6
Figure 4.13 Fast Opto-Isolated Serial Interface Signal Waveforms
NAME
t1
t2
t3
t4
t5
t6
t7
MIN
NOM
MAX
Units
ns
ns
ns
ns
ns
ns
ns
COMMENT
5
5
5
10
10
10
20
FSDO/FSCTS hold time
FSDO/FSCTS setup time
FSDI hold time
FSDI Setup Time
FSCLK low
FSCLK high
FSCLK Period
Table 4.6 Fast Opto-Isolated Serial Interface Signal Timings
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