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Theory of Operation
Detailed Circuit Description
2
2-23
The clock for the Ethernet Chip is provided by A1Y2, A1C38, and A1C89, which are
connected directly to A1U32-17 and A1U32-18. This provides a 20 MHz clock to the
Ethernet Chip. The clock allows the Ethernet Interface to send and receive data at
10 M-bits per second.
A1R107 sets internal bias currents in the Ethernet Chip (A1U32). The voltage drop
across this resistor is normally around 1.25 volts.
The Ethernet Chip also drives three LEDs. A1DS2 indicates that a packet is being
received. A1DS3 indicates that the Ethernet Chip is transmitting a packet. A1DS1
indicates two different things depending on the type of physical interface being used. If
10BASE-2 (Coax) is being used, A1DS1 indicates when collisions were detected on the
Ethernet. If 10BASE-T (Twisted Pair) is being used, A1DS1 indicates whether the link
to the host computer is intact. A1DS1 is driven by the Ethernet Chip (A1U32) through a
dual diode (A1CR4), which ORs together two outputs (A1U32-59 and A1U32-60).
A1DS2 and A1DS3 are driven directly by A1U32-57 and A1U32-58. Resistors A1R37,
A1R122, and A1R121 limit current to LEDs A1DS1, A1DS2, and A1DS3.
Ethernet Connectors The instrument is connected to the Ethernet by either a
10BASE-2 interface (A1P2) or a 10BASE-T interface (A1P1). 10BASE-2 uses coaxial
cable to attach instrument to a host computer. Other instruments and possibly other
equipment may be attached to the same coaxial cable when a 10BASE-2 interface is
used. 10BASE-T uses twisted pair cable to attach instrument to some kind of hub. A host
computer, other instruments, and other equipment are connected to a 10BASE-T hub
using separate twisted pair cables.
10BASE-T Ethernet Connector Pulse transformer A1T4 provides electrical isolation
between the Ethernet Chip (A1U32) and the 10BASE-T connector (A1P1). Two twisted
pairs are used in a 10BASE-T cable. One pair is used to transmit data (A1P1-1 and
A1P1-2), and the other is used to receive data (A1P1-3 and A1P1-6). Resistors A1R86,
A1R95, and capacitor A1C60 provide a termination network for data received through
the pulse transformer (A1T4). Resistors A1R32, A1R76, A1R92, A1R100, and A1R120
provide a termination network for data transmitted through the pulse transformer
(A1T4). Connector A1P1 provides chassis potential on pins 9 and 10 to shield the cable
and provide a system ground. Capacitor A1C28 helps the instrument meet EMI
requirements.
10BASE2 Ethernet Connector Ethernet transceiver chip A1U16 drives and receives data
on the 10BASE-2 (Coaxial) interface connector (A1P2). In addition, A1U16 detects
collisions on the Ethernet. Data and collision detect signals are transferred between the
transceiver chip (A1U16) and the Ethernet Interface (A1U32) through pulse transformer
A1T3. Power supply module A1U38 provides a -9V isolated power supply to the
10BASE-2 transceiver chip A1U16. The power supply module can be powered down by
a signal from the Ethernet Chip (A1U32-64) when the 10BASE-2 interface is not being
used. The transceiver chip (A1U16) is protected from electrostatic discharge (ESD) by
resistors A1R136, A1R77, capacitors A1C23, A1C61, and MOV A1RV2. A1R18 sets
internal bias currents in A1U16.
Содержание NetDAQ 2640A
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Страница 243: ...Schematic Diagrams 7 7 11 Figure 7 2 A2 Display PCA Assembly cont 2620A 1002...
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