Mmu Block Diagram - Tandy 26-3334 Service Manual

As it
is
clear from
the
Memory
Map,
the
memory area
of the CoCo3
is
from
&00000 through &7FFFF (512K bytes).
The Memory Management Unit
(MMU)
inside of
the
TCC1014, pins FFAO
through FFAF, selects A13 -
A18
(actually A16 -
A18). Figure 5-7
shows the Block Diagram
of
the
MMU.
00-D5
AI3-AI5
(CPU
Address)
and
TR
(FF9I
)
A0-A3
(CPU Address)
MMUW
AI3-AI8
Figure 5-7. MMU Block Diagram
2)
Video Generation Circuit
For NTSC Version
In
Color Computer
2,
the
composite
video signal
is
created
in
Modulator
IC
(MC1372), while
the
intensity
control signal
(Y) and the color
information signals
J0A
and 0B are
generated
in
VDG (MC6847).
In
Color
Computer
3,
all of these signals are
generated
in
ACVC
(IC6), and
output
from pin
65 as the
composite video
signal. This signal
is
provided
to
the video output terminal through
buffer
(Q2,
Q3) and to the modulator.
For PAL Version
The ACVC
is
designed
to
output both
composite video signal and analog RGB
signal. Since composite video signal
is
specially designed
for
NTSC
systenij the
PAL Encoder circuit
is
used
to
encode the RGB signal
to the
PAL signal. For
this
purpose,
the
VSYNC and HSYNC output from pins
55
and
56 of IC6 are
provided
to the
PAL
Encoder
as
a
composite sync signal
through
the
inverter IC15
and
mixing
circuit
(Qll,
D15
- D17). The
output
of PAL Encoder, that
is
the
PAL
system composite video signal,
is
then provided
to the
RF Modulator via
buffer
Q3,
and
to the
video
output
terminal via Q3 and
Q2.
ACVC also contains analog RGB output
and
a
total of
64
color selections.
For
the
video generation circuit
where
the control register
is
designated via software, please refer
to the
Memory Map
in
section
1.3.
3)
Interrupt IN/OUT
In CoCo2,
the three interrupt sources
CART*, HSYNC* and VSYNC requested
an
interrupt
to the CPU from
PIA
as
IRQ*
and FIRQ*.
In r
Co3, in
addition
to
the
above mentioned interrupt
sources,
an
interrupt
to the CPU can
be
requested
as IRQ-*
or
FIRQ* from
serial
I/O, keyboard, and 12-Bit
interval
timer.
It
has higher
selectivity. Refer
to FF90 and FF92
through FF95
in the
Memory
Map,
-37-