User guide

WA_DEV_FEX20_UGD_002 Rev 004 March 08, 2011 34
Fastrack Xtend User Guide
Interfaces
Vref sets the reference voltage of the input or output of the two GPIOs. Leaving it unconnected sets
the GPIO level at 2.3V – 2.6V by default. It is strongly recommended to connect to the required
GPIOs‟ output voltage (2.8V ~ 15V).
Refer to the following table for the pin description of the GPIOs.
Table 9. GPIO Pin Description
Pin #
Signal
I/O
I/O Voltage
Description
1
GPIO21
I/O
Vref
General purpose input/output
2
GPIO25
I/O
Vref
General purpose input/output
3
Vref
I
2.8V ~ 15V
Voltage reference for the GPIOs
Note: It is recommended to use a 6-wire cable accessory for easy access to these three lines. Please
refer to section 14.1 Standard Accessories for more information about the 6-wire cable accessory.
When the voltage reference, Vref, is not connected, if one of the GPIO output is in High state while
the other is in Low state, the GPIO in high level voltage will be at 2.3V.To avoid this voltage drop, it
is recommended to use Vref to the desired output voltage.
With Vref connected to 2.8V, both GPIO21 and GPIO25 may be interfaced with a component that
complies with the following levels.
Table 10. GPIO Pin Operating Conditions when Vref is at 2.8V
Parameter
Mininum
Typical
Maximum
Condition
V
IL
0.84V
Please refer to Figure 7.
V
IH
1.96V
Please refer to Figure 8.
V
OL
0.4*
Please refer to Figure 9.
V
OH
2.8*
FXT Zout = 100K Pull-up to Vref, please refer to
Figure 10.
* Value without external load.
Figure 7. Equivalent Circuit of V
IL
, Vref = 2.8V