Microchip Technology GridTime 3000, Руководство по установке

Страница: 42 / 302

6.6.2.3.1 Cable Recommendations
This section describes how to select a cable to use with the GridTime 3000 BNC ports.
Cable Type — Shielded Twisted Pair (STP) or Coaxial
Either Coaxial or shielded twisted pair (STP) cables can be used with the BNC ports if they have been terminated
with a female BNC connector.
STP cable use is recommended over Coaxial cable, as Coaxial cable introduces more line capacitance than STP.
Capacitance reduces the cable lengths that can be used before excessive signal loss occurs.
The effects of a high line capacitance can round the edges of TTL signals, which can reduce time accuracy, and in
extreme cases can cause end devices to falsely trigger rising or falling edges, preventing the device from reliably
decoding signals.
Figure 6-13. Signal rounding caused by the high capacitance of a Coaxial cable
8
6
4
2
0
-2
-4
Cable Frequency Rating
The frequency rating of the cable used should exceed the highest frequency content of the output signal. For
AM-IRIG this is 1 kHz, for fixed frequency sine waves it is the configured fixed frequency (1.544, 2.048 or 10MHz),
for fixed frequency square waves and TTL signals this will be far higher due to the harmonics introduced by the sharp
edges (~1 MHz).
6.6.2.3.2 Output Circuitry Recommendations
This section describes best installation practices for output circuity connected to the GridTime 3000's BNC ports.
Topology Recommendations
Connecting a Single End Device to a port
If the connection from the BNC port needs to go to only a single device, make a direct connection between the BNC
port and the port of the end device, and put a termination resistor in parallel with the cable. Ensure the cable and end
device input meet the
6.6.2.3.1. Cable Recommendations below.
Connecting Multiple End Devices to a port
If multiple end devices need to be connected to a single BNC port, connect the end devices in parallel along a single
bus, with a termination resistor also in parallel. Refer to
6.6.2.3.1. Cable Recommendations to determine how many
devices can be used on the bus, and the wire length restrictions on the bus.
The circuitry should use a multi-dropping topology, not a star topology.
Installation
©
2022 Microchip Technology Inc.
and its subsidiaries
Manual
DS00004572A-page 42