Rev 1.0
1/27/14
17
17
Reference Guide
Interfaces
Refer to the following table for the pin description of the GPIOs.
Table 3.
GPIO Pin Description
Pin #
Signal
I/O
I/O Voltage
Description
1
GPIO25/INT 1
I/O
Vref
General purpose input/output or Interrupt
2
GPIO35
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 the Getting Started Guide at
http://www.usr.com/support/3500
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 GPIO35 and GPIO25 may be interfaced with a
component that complies with the following levels.
Table 4.
GPIO Pin Operating Conditions when Vref is at 2.8V
Parameter
Mininum
Typical
Maximum
Condition
V
IL
0.84V
Please refer to Figure 6.
V
IH
1.96V
Please refer to Figure 7.
V
OL
0.4*
Please refer to Figure 8.
V
OH
2.8*
modem Zout = 100K Pull-up to
Vref
, please
refer to Figure 9.
*
Value without external load.
Figure 6.
Equivalent Circuit of V
IL
,
Vref
= 2.8V