Vector Graphic Bitstreamer II User Manual - page 30
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Vector Graphic Bitstreamer II
BOard
Use a 25-wire ribbon cable, with male 08-25 connectors at both ends.
(TI
810 has
a female
connector
at its rear, as does the Bitstreamer II Serial
I/O cable.)
On both ends of this male-to-male
cable,
pin
1 is the upper
left-hand
pin when
looking
toward
the connector's
pins
and holding t.'e
connector so that the longer reM of pins is on top.
Alternately,
you can
create
a 2 wire
cable
connecting
lines 3 and 7
straight through, and using a male 06-25 at both ends, as described
above.
In addition,
you MUST
solder
a jumper
between
pins
6, 8, and
9 at the
printer end of the cable,
in order
to enable
the pr inter.
(The printer
provides +12 VDC on line 9, and requires +12 VDC on lines 6 and 8.)
Since
the TI 810 printer
can
no faster
than 150 characters per
second, which corresp:mds to 1500 baoo, transmittin; at a rate of 2400
baud
is too fast
for the printer
using
the cable
connection
described above.
However, the TI 810 can receive at up to 9600 baud.
This is feasible if the
computer
monitors
line 11 coming fran the printer.
The printer pulls line
11 down to -12 VOC when it cannot accept any more characters, and otherwise
holds
line
11 at +12 VDC.
Line 11 is called "printer busy status."
Since
RS-232C line 11 is not brought onto the board by t.'eBitstreamer
II Serial
I/O cable,
you have
to string
a wire
from
the RS-232C
connector
to the
Bitstreamer II board.
Connect this line to t.lle
input of the spare
RS-232C
line
receiver
(U26 pin 1) and connect the output of this receiver
(U26 Qin
3) to pad 1 of jumper area P, 0, or N (depending on whether
you are
USin3
serial
channel
A, B, or C respectively.)
Then cut the trace which leads
from this jumper pad to ground, on the back side of the board.
~1at the above accomplishes is to connect the printer OlSY status line to
the CTS input of the 8251 so that when the printer signals it cannot
accept
more
characters,
CTS is pulled up, ~1ich disables the 8251 transmit circuit
which in turn prevents software from sending characters
to the 8251.
This
assumes
the software polls the 8251 TxRDY status bit or is interrupt driven
by t.'eTxRQY line.
The former is true for all serial printer
drivers
from
Vector Graphic at the ti~
of this writing.
When
the computer is sending a great deal of data to the TI 810 directly
from memory 'liithoutany [)auses at all,
even 1200
baud
is too
fast.
The
result
will
be occasional
loss of a line of output.
TI1is will not happen
with most business softwa re or program
assembly,
because
there
are many
pauses
for disk
access
and/or
calculation.
It may happen
however when
printin3 edit~r or word processor text directly fraTIma~ory.
If you
expect
to encounter
t.,is,install the oodification given above under "2400 baud or
more" if the printer is used at 1200 baud.