Vector 4 - Page 34

VECTOR 4
TECHNICAL INFORMATION
1.1 HOW THE VIDEO AND CPU CYCLES
ARE COMBINED
Summary: The Vector 4 functions by using two different cycles or
time slots: YIDEO and CPU. Specific clocking and timing signals are
generated so that these cycles are maintained.
During
the
Video
cycle
the
data
on
the
address
bus*
is
from
the
Video
System
and
during
the
CPU
time
slot
the
SBC
address
bus
contains
addresses
which
will
be
used
directly
by
the
microprocessor(s).
This
is
done
because
both
these
systems
use
the
same
block
of
RAM
Memory.
Section
1.1-B
describes
each
cyecle
and
discusses
how
the
cycles
relate
to
the
operation
of
the
complete
system.
Exhibit
[I-2
gives
a
pictorial
representation
of
the
timing
cyecles.
4. Clock
An oscillator generates a 32.64 MHz (32M) signal which is sent to a synchronous
counter (U115), the Video Subsystem (used as a dot clock), and to a group of
FFs Wthh generate the clock for the Microprocessors (Signals CLOCK and
CLOCK| **).
The synchronous counter divides the 32.64 MHz signal into several signals which
are used for particular timing functions. These latter timing signals along with
other 31gnals generated by the clock subsystem are described below (See Tnmmg
Diagram in Exhibit VI-3).
2M, 4M
8M, 16M These signals provide 2MHz, 4MHz, 8MHz and 16MHz clock rates for
all the major subsystems.
LATCH This signal is used within the CPU MUX Subsystem (<B8>). It
clocks the lateh (U34) so that 16 bits of data (coming from U33 and
U17) are multiplexed to Data Bus lines 0 thru 7. This multiplexing
occurs during the T3 state of the YIDEO Cycle.
The LATCH signal is also used by the Video System as a character
latch. It is routed to the two video shift registers (KC5>) where it
clocks in one row (a scan line for one character cell) consisting of
16 bits. Its period is lus with a duty cycle of approximately 62 ns.
* The Vector 4 uses several different types of "Buses". The bus structure is
shown in Exmmt__IL_i and described in S_ec_tmn_l.z
** The "|" means the signal is active LOW.
09-01-82 7200-0001 II1-5