∘
Bits
0
—4 of port
B
can be used as Kempston-compatible Joystick interface.
Resistors
R99:106
ensure a “
0
” reading in stand-by, resistor
R107
ensure a
“1” level through one of the joystick contacts.
∘
Bits
0
—2 of port
C
are used for storing the
BORDER
color.
∘
Bit 3 serves as output for tape recording. Resistors
R97
,
R98
and diodes
D06
,
D07
ensure an optimum level for the majority of tape recorders.
∘
Bit 4 is used as audio output. The
i8255
circuit can directly drive a
telephone speaker through
C45
, speaker mounted in the microcomputer's case.
Bit 5 is a general use output bit. Can be used as a protocol line for port
∘
B
.
Bit 6 is an output line. It indicates the configuration selected at startup. In
∘
a particular configuration it can be used as a general use bit.
Bit 7 is a serial output. It is separated and inverted by
∘
U87/11
, the level
being adapted by
T2
to be
RS-232C
compatible. It is used as a serial data
transmission bit to a printer or another computer, using an emission routine.
The floppy disk interface is built on a separate board using the dedicated
floppy disk controller circuit
i8272
.
To be able to use the features of
Mode 2
Interrupts of the microprocessor,
the interrupts generated by
i8272
are passed through the counter/timer
channels circuit
Z80-CTC
(
U01
). This circuit has four counters of which counters
0
to 2 are cascaded. By programming, channel
0
CTC
generates one interrupt
for each byte to be transferred between
i8272
and microprocessor; channels 1
and 2 cascaded generate an interrupt at the end of the sector also generating
the Terminate Count (
TC
) signal for
i8272
. In this hardware configuration,
i8272
can be programmed to work without direct memory access, simplifying
the interface very much.
The floppy disk interface block diagram is shown in
Fig.9
.
The clock signal generated by the 16 MHz quartz oscillator is divided by 2 or by
4 depending on the position of the switches
SD0-3
and is used as a clock for
i8272
. Remarkable is this original configuration where
i8272
- by means of the
selection signals
US0
,
US1
- selects its own 8 or 4 MHz clock frequency for work
with
8”
or
5¼”
floppy drives. This configuration allows the use of 2 floppy drives
simultaneously regardless of their sizes, without having to intervene by means
of software to switch the clock frequency to the floppy disk controller.
The circuit made with
U04/9
and
U03/4
performs the multiplexing for
READY
signals coming from floppy drives.
The double decoder circuit
U05
generates
SELECT
signals for floppy
drives, as well as
HEAD
LOAD
signals for the reading/writing heads of the drives.
Signals
HL0-3
(
HEAD
LOAD
) can also be used as
MOTOR
ON
signals for
5¼”
floppy drives which have this input line.
17
Содержание CoBra
Страница 20: ...Fig 10 Keyboard schematic 20 ...
Страница 21: ...Fig 11 Keyboard schematic 21 ...
Страница 23: ...Fig 13 Power source schematic 23 ...
Страница 39: ...9 APPENDIX 1 CoBra Microcomputer Schematics 39 ...
Страница 40: ...Fig A1 1 CoBra Microcomputer Central Processing Unit 40 ...
Страница 41: ...Fig A1 2 CoBra Microcomputer Configurator and Selector Circuit 41 ...
Страница 42: ...Fig A1 3 CoBra Microcomputer Read Only Memory Circuit 42 ...
Страница 43: ...Fig A1 4 CoBra Microcomputer DRAM Memory Circuit 43 ...
Страница 44: ...Fig A1 5 CoBra Microcomputer Memory Access Prioritizer and Command Logic 44 ...
Страница 45: ...Fig A1 6 CoBra Microcomputer Video Address Generator Circuit 45 ...
Страница 46: ...Fig A1 7 CoBra Microcomputer Video Address Multiplexer Circuit 46 ...
Страница 47: ...Fig A1 8 CoBra Microcomputer Video Memory Circuit 47 ...
Страница 48: ...Fig A1 9 CoBra Microcomputer Video Sync Pulses Generator Circuit 48 ...
Страница 49: ...Fig A1 10 CoBra Microcomputer Video Signal Shape Generator 49 ...
Страница 50: ...Fig A1 11 CoBra Microcomputer Interfaces 50 ...
Страница 51: ...Fig A1 12 CoBra Microcomputer Voltage Level Adapter Circuits 51 ...
Страница 52: ...Fig A1 13 CoBra Microcomputer Keyboard Interfacing Circuit 52 ...
Страница 53: ...Fig A1 14 CoBra Microcomputer TV Monitor Interfacing Circuit 53 ...
Страница 55: ...10 APPENDIX 2 Flopppy Disk Interface Schematics 55 ...
Страница 56: ...Fig A2 1 Floppy Disk Interface Disk Controller 56 ...
Страница 57: ...Fig A2 2 Floppy Disk Interface Command and Control Signals Generator Circuits 57 ...
Страница 58: ...Fig A2 3 Floppy Disk Interface Write Clock and Digital PLL Circuits 58 ...
Страница 59: ...10 APPENDIX 3 Component Placement on Boards 59 ...
Страница 60: ...60 Fig A3 1 Component Placement on Keyboard Circuit Board ...
Страница 61: ...61 Fig A3 3 Keyboard Circuit Board top layer seen from above keys side ...
Страница 62: ...62 Fig A3 3 Keyboard Circuit Board bottom layer seen from above keys side ...
Страница 63: ...Fig A3 5 Component placement on the floppy interface board 63 ...