TM8000 3DK Hardware Developer’s Kit
Application Manual
Programmable I/O Lines
67
September 2003
© Tait Electronics Ltd
Special Purpose
Outputs
AUX_GPIO4 can be used as a general purpose output with normal drive
levels, or it can be configured as a high current sink output capable of
directly driving external devices. To configure high current sink, a high
power transistor must be soldered to the main board assembly. For more
information refer to
“Connecting an External Alert Device” on page 133
Momentary or
Latching
Output signals are latching or momentary, depending on their function.
Examples: ‘
Control Status Rx (Line 1 to 3)
’ is always latching. Most of the
other output signals are momentary. ‘
’ can be either
latching or momentary.
Power-Up
Considerations
During power-up of the radio, any I/O lines configured as outputs are in an
uncontrolled and high-impedance state. The pullup resistors have a
dominant effect and thus all outputs will appear as if they are indicating logic
high during this period.
The radio will not actively control these lines for up to 1 to 2 seconds after
power is first applied or the radio has been switched on. It is therefore
important to consider how this will affect application circuitry interfaced to
the radio and take measures to manage what happens during this transition.
Defining the active state of the outputs as logic low may provide suitable
protection, as outputs will appear inactive during radio power-up. In other
cases it may be necessary to buffer the outputs with suitable circuitry to
isolate application circuits from the radio signals during this transition.
Figure 3.11
Momentary and latching output signals
input
output
output
t
t
t
(momentary)
(latching)
