Vector Graphic Bitstreamer II, User Manual, Page: 21 / 54

In general,. Vector Graphic software has been written so that different
types of devices are controlled by different serial channels on the
Bitstreamer II board. For example, at the time of this writing, any
Extended Systems Monitor having option C enables a standard serial terminal
to be plugged directly into serial channel A. The Version 4 Extended
Systems r1onitor (any option) contains a program that enables the operator to
communicate to a time share service via a modem connected via an RS-232C
cable to serial channel B, tNhich has to be converted to a DTE channel first.
Lastly, operating systems such as MOOS and CP/M from Vector Graphic, and
Vector Graphic's WOrd Managagment System, output to printers via serial
channel C, and in some cases, if you desire, via channel A instead.
28
M
current loop
Serial Channel C can be IOOdified with a jumper to communicate using 20
IDA
current loop. Details are given in Section 2.6.
1.9 Real time clock interrupts
The board has a 55 Hz (pulses per second) real-time clock. Connected to
this clock is a component (called the "real-time clock latch") which becomes
active and stays active as soon as it receives a pulse from the clock. The
output of this latch can then be connected to the interrupt line, along with
or instead of the 8251 lines. Jumpers pads are provided. This enables you
to create software Yrhichresponds to interrupts arriving every 1/55 of a
second, such as multi-user or multi-tasking software.
Your interrupt service routine, the routine that is called in response to
the interrupt, must deactivate (reset) the real-time clock latch before
re-enabling interrupts. If it does not do this, the latch will immediately
cause another interrupt, even though the clock has not produced another
pulse. To do this, execute an input instruction frQn Parallel Channel 8 on
the 8i tstreamer II Board. (Parallel channels are discussed later in
Perspective.) You do not use the inputted data, you only input it and then
ignore it. The action of inputting fram this channel resets the real-time
clock latch. If you are using the real-time clOCk on the Bitstreamer II as
a source of interrupts, you can still use the input side of Parallel enannel
B for real inputting of data at other tLnes.
Details of wiring and using real time clock interrupts with this board
are given in Section 2.7.