Gate
U87/8
turns off the electron beam in the monitor during the
horizontal-retrace. The outputs of
U85
are normalized in order to yield the
intensity signal, and separated through
U86
to yield the
R
,
G
,
B
,
I
and sync
signals for the color monitor.
U88/11
along with
T1
generates the
B/W
composite video signal.
The oscillator made of
U88/6
,
U88/8
is controlled by the
FD7
signal,
together with gate
U88/3
achieving the
FLASH
function. Resistor
R43
ensures
the blinking oscillator is in sync with the TV vertical sync signal. Its value must
be chosen so that the oscillator flips during any TV line except the 192 ones
that are visible.
The diode gates that synthesize the
BD6N
signal, along with
R73
, achieve
the
BRIGHT
function, at the same time suppressing it for color black.
Circuits
U12
and
U13
and gates
U16
,
U14
make up a divider by 56. The
outputs of this divider are being used as character address for the video
controller and are the basis for horizontal sync and retrace signals. The
associated signal timings are shown in
Fig.7
.
Fig. 7 - The timings for TV line signals
Circuits
U32
,
U33
,
U15/9
and gates
U37
,
U34
make up a divider by 312,
their outputs being used as a TV line address, character row address and
screen third address on one hand, and on the other hand they are the basis for
generating the
NBRD
and
NVS
vertical sync signals.
The associated timings are shown in
Fig.8
.
15
Summary of Contents for CoBra
Page 20: ...Fig 10 Keyboard schematic 20 ...
Page 21: ...Fig 11 Keyboard schematic 21 ...
Page 23: ...Fig 13 Power source schematic 23 ...
Page 39: ...9 APPENDIX 1 CoBra Microcomputer Schematics 39 ...
Page 40: ...Fig A1 1 CoBra Microcomputer Central Processing Unit 40 ...
Page 41: ...Fig A1 2 CoBra Microcomputer Configurator and Selector Circuit 41 ...
Page 42: ...Fig A1 3 CoBra Microcomputer Read Only Memory Circuit 42 ...
Page 43: ...Fig A1 4 CoBra Microcomputer DRAM Memory Circuit 43 ...
Page 44: ...Fig A1 5 CoBra Microcomputer Memory Access Prioritizer and Command Logic 44 ...
Page 45: ...Fig A1 6 CoBra Microcomputer Video Address Generator Circuit 45 ...
Page 46: ...Fig A1 7 CoBra Microcomputer Video Address Multiplexer Circuit 46 ...
Page 47: ...Fig A1 8 CoBra Microcomputer Video Memory Circuit 47 ...
Page 48: ...Fig A1 9 CoBra Microcomputer Video Sync Pulses Generator Circuit 48 ...
Page 49: ...Fig A1 10 CoBra Microcomputer Video Signal Shape Generator 49 ...
Page 50: ...Fig A1 11 CoBra Microcomputer Interfaces 50 ...
Page 51: ...Fig A1 12 CoBra Microcomputer Voltage Level Adapter Circuits 51 ...
Page 52: ...Fig A1 13 CoBra Microcomputer Keyboard Interfacing Circuit 52 ...
Page 53: ...Fig A1 14 CoBra Microcomputer TV Monitor Interfacing Circuit 53 ...
Page 55: ...10 APPENDIX 2 Flopppy Disk Interface Schematics 55 ...
Page 56: ...Fig A2 1 Floppy Disk Interface Disk Controller 56 ...
Page 57: ...Fig A2 2 Floppy Disk Interface Command and Control Signals Generator Circuits 57 ...
Page 58: ...Fig A2 3 Floppy Disk Interface Write Clock and Digital PLL Circuits 58 ...
Page 59: ...10 APPENDIX 3 Component Placement on Boards 59 ...
Page 60: ...60 Fig A3 1 Component Placement on Keyboard Circuit Board ...
Page 61: ...61 Fig A3 3 Keyboard Circuit Board top layer seen from above keys side ...
Page 62: ...62 Fig A3 3 Keyboard Circuit Board bottom layer seen from above keys side ...
Page 63: ...Fig A3 5 Component placement on the floppy interface board 63 ...