Frontplane circuits include
the
LAN chip set, timer,
and
the
transceiver chip.
The
LAN chip set
serves
the
dual
function of a DMA controller
and
an
Ethernet/EEEE
802.3 controller.
Encoded
data
from
the
SIA is
transmitter
by
the
transceiver chip.
Data
from
the
network is sent by
the
transceiver chip
to
the
SIA.
The
LAN
portion
of
the
board
is software compatible
with
the
HP
98643
LAN/300
Link
Card.
Eight
DIP
switches on
the
system interface
board
control
the
following LAN functions:
• Select Code, 0
through
3l.
•
Interrupt
Level, 3
through
6.
• Local/Rernote.
Switches for LAN interface configuration are explained Table 3-8. Refer
to
the
picture
of
the
system interface
board,
Figure 3-22 for its location.
RS-232 Interface
An RS-232 Interface section is
part
of
the
system interface
board's
electronics. Using
an
INS8250
UART,
it's
almost identical
to
the
HP
98644A RS-232 Serial Interface
Card.
It
differs from
the
HP 98644A Interface
Card
in
that
it:
• Allows
interrupts
at
level 5 only.
There
are no switches
to
change
the
interrupt
level is
the
same as
the
HP
98644 Card.
•
Permanently
sets
the
select code
to
9.
The
HP
98644
card
has
switches which allow
this
address
to
be changed.
• Does not allow reconfiguration
to
change
the
RS-232's ID
to
that
of
the
HP
98626 card.
Three
switches on
the
system interface
board
are
associated
with
RS-232. Located on
the
HPIB/RS232
configuration switch,
they
perform
the
following functions:
• REM - Controls
the
local/remote
bit
in
the
ID register.
• MEN
--
Sets
the
handshake
input
lines
to
their
default condition, all ones.
• DIS
--
Disables
the
RS-232
at
select code 9 so
it
won't
be
found. all ones.
In
addition
to
the
registers built into
the
INS8250 UART, two
external
register have also been
implemented.
Both
sets of registers
are
multi-mapped
within a 64
Kbyte
region of memory
associated
with
I/O
select code
9.
Functional Description
103
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