FT2232C Dual USB UART / FIFO I.C.
Reset / Enable
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 AN2232C-02, “Bit Mode
Functions for the FT2232C” for more details and examples.
Figure 36 - Fast Opto-Isolated Serial Interface Example
VCC5V
Cable
VCCE
FT2232C
8
HCPL-2430
1
2
1K
1K
7
40
39
470R
470R
FSDI (BDBUS0)
DI
3
6
5
CLK
FSCLK (BDBUS1)
4
VCCE
VCC5V
8
1
HCPL-2430
1K
1K
7
470R
470R
38
37
2
3
FSDO (BDBUS2)
FSCTS (BDBUS0)
DO
6
5
CTS
4
In the example shown in figure 12 two Agilent HCPL-2430 (see the semiconductor section at www.agilent.com) high
speed opto-couplers are used to optically isolate an external device which interfaced to USB using the FT2232C. In
this example VCC5V is the supply for the FT2232C (bus or self powered), and VCCE is the supply to the external
device.
Care must be taken with the voltage used to power the photoLED’s. It should be the same supply that the I/Os are
driving to, or the LED’s may be permanently on. Limiting resistors should be fitted in the lines that drive the diodes.
The outputs of the opto-couplers are open-collector and so need a pullup resistor.
Testing
Fast serial mode has been tested using an Scenix (Ubicom), SX28 microcontroller (see www.ubicom.com) which
was configured in loopback mode. This was done both with, and without HP HCPL-2430 opto-isolators in place. The
isolators add a considerable delay to the turnaround time seen by the micro. This was close to 100 nS with the high
speed HCPL-2430 device. This is the combined delay of the clock signal from the microcontroller going through
an opto-coupler to the chip, and the data from the FT2232C chip going through the other opto-coupler back to the
microcontroller.
DS2232C Version 1.2
© Future Technology Devices International Ltd. 2004
Page 52 of 54
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