![Rabbit Rabbit 4000 Скачать руководство пользователя страница 211](http://html1.mh-extra.com/html/rabbit/rabbit-4000/rabbit-4000_user-manual_3116714211.webp)
201
20. 10B
ASE
-T E
THERNET
20.1 Overview
Network Port A implements all of the required digital elements of the 10Base-T standard,
and is normally used with two channels of the DMA controller. The receiver provides 32
bytes of buffering, and the transmitter has 16 bytes of buffering. Network Port A connects
externally through six dedicated pins. The network port can operate in either half-duplex
or full-duplex mode, selected via auto-negotiation.
The network port requires an accurate 20 MHz clock to generate the 10 Mbits/s serial rate
of 10Base-T. This clock can come from the main system clock or a dedicated 20 MHz
input under program control. The clock for the network port may also be disabled to con-
serve power. The network port contains synchronization circuitry to allow operation from
the 20 MHz reference clock while the main system clock runs independently.
The network port transmitter precedes the transmit data automatically with a preamble and
start-frame-delimiter, and appends CRC and the end-frame-delimiter after the last byte.
Frame transmission starts automatically once the transmit FIFO is full and any interframe
gap time or back-off time has expired. Transmission is aborted if a collision is detected,
and is retried up to 16 times using the standard random back-off time algorithm. Detection
of a collision causes the transmitter to send a 32-bit “jam” pattern of all ones to guarantee
that all receivers in the network recognize the collision. The transmitter uses the 10 most-
significant bits of the CRC checker, starting with bit 22 and increasing, to generate the initial
seed for the back-off algorithm. Collisions that occur later than one slot time (512 bit times)
are reported as late collisions, but are otherwise treated identically to “normal” collisions.
If a transmission is not successful after 16 attempts, the transmitter halts and reports the
failure via an interrupt. The transmitter guarantees the 9.6 µs inter-frame gap and imple-
ments the fair-access algorithm within the inter-frame gap. The transmitter automatically
sends link test pulses, even while otherwise disabled, every 16.0 ms. The transmitter con-
tains a jabber timer, which automatically disables the transmitter after 26.2 ms of continu-
ous transmission. This error condition generates an interrupt and must be answered by
resetting the network port. The corresponding DMA channel is automatically halted by
this error condition and must be restarted after the network port has been reset.
The Rabbit 4000 does not implement the 10Base-T physical layer on-chip, but provides
differential transmit data to simplify the external circuitry required to drive the 10Base-T
cabling with the required waveform.
Содержание Rabbit 4000
Страница 1: ...Rabbit 4000 Microprocessor User s Manual 019 0152 070720 H...
Страница 18: ...8 Rabbit 4000 Microprocessor User s Manual...
Страница 40: ...30 Rabbit 4000 Microprocessor User s Manual...
Страница 74: ...64 Rabbit 4000 Microprocessor User s Manual...
Страница 82: ...72 Rabbit 4000 Microprocessor User s Manual...
Страница 86: ...76 Rabbit 4000 Microprocessor User s Manual...
Страница 96: ...86 Rabbit 4000 Microprocessor User s Manual...
Страница 182: ...172 Rabbit 4000 Microprocessor User s Manual...
Страница 240: ...230 Rabbit 4000 Microprocessor User s Manual...
Страница 248: ...238 Rabbit 4000 Microprocessor User s Manual...
Страница 256: ...246 Rabbit 4000 Microprocessor User s Manual...
Страница 310: ...300 Rabbit 4000 Microprocessor User s Manual...
Страница 330: ...320 Rabbit 4000 Microprocessor User s Manual...
Страница 348: ...338 Rabbit 4000 Microprocessor User s Manual...