T801-4 Installation and Operation Manual
Description
21
© Tait Electronics Limited September 2007
PORT B - RSU
This RJ45 connector provides the RS-485 interface to the QS
2
RSU
(remote site unit). It is used as the input for the signal from the GPS module
in the RSU. It provides connections for the following signals:
■
a 1PPS RS-485 data pair input at standard RS-485 levels
■
a 1PPS RS-485 data pair output/input at standard RS-485 levels
■
a 1PPS VALID input
■
a 1PPS VALID output/input.
This port is generally referred to as “
PORT B
” in the rest of this manual. The
pin allocations for this RJ45 connector are given in the following table.
They are compatible with the QS
2
RSU.
g
Pin
Signal Name
Signal
Type
Logic
Notes
1
1PPS+ EXTNL B
input
1PPS RS-485 input
2
1PPS– EXTNL B
3
not connected
4
1PPS VALID I/O
output/
input
ab
Output:
internal pull-up resistor to 3.3V;
output low = 1PPS valid;
maximum input voltage = 8V;
maximum sink current = 18mA;
output low level <0.4V for 1.8mA sink
current
Input:
maximum input voltage = 8V;
input low level (<0.8V) = 1PPS valid
5
1PPS VALID IN
input
b
active low (<0.8V) = 1PPS
valid
input connection for VALID signal (from
QS
2
RSU);
c
internal pull-up resistor to 3.3V;
maximum input voltage = 9V
6
GND
ground
7
1PPS RS-485+ OUT output/
input
d
1PPS RS-485 output
(or input)
8
1PPS RS-485– OUT
a. The factory default is an output. Can be configured as an input using DIP switch 1 (refer to
“DIP SWITCHES” on
page 22
).
b. Can be configured to accept the pulsed signal from the QS
2
RSU with version 3.00.00.00 and later firmware (one
pulse per 10 seconds).
c. Compatible with the 1PPS VALID signal from the QS
2
RSU, whether it is steady or pulsed.
d. The factory default is an output, with the option of disabling when the GPS fix is deemed invalid. Can be config-
ured as an input using internal links (refer to
“Setting the Links on the System Interface Board” on page 50
). You
cannot use the T801-4 to provide a 1PPS signal to the QS
2
RSU with v3 and later firmware. Although this port
provides a 1PPS RS-485 output, the associated VALID signal (TTL steady state level) is not compatible with v3
firmware, which is designed for a pulsed VALID input. Refer to the RSU Service Manual for more information.
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external view
