Fig. 3 - Memory configuration switching sequence
The diode
D02
makes sure the microprocessor exits the reset state a few
miliseconds before the
NPOR
signal turns off. During this time the
microprocessor executes the first instructions where bit 7 of the
R
register is
set to “1”, which makes sure the flip-flop
U36/5
is maintained at “1” after
NPOR
turns off. This is the temporary startup configuration, where the memory map
allows the microprocessor to access the
BOOT
EPROM
U89
, the 16k
BASIC
EPROM
,
the video memory and the 16k
DRAM
(
BANK #0
). In this startup configuration,
the
RESET
button is not to be used, because the contents of the
R
register
would be erased, which leads to a random memory configuration. The user can
choose the configuration wanted by pressing one of the following keys:
— B for BASIC interpreter resident in EPROM;
— C for BASIC or other operating system resident on magnetic tape;
— W to check the contact between the EPROM memories and their
sockets. The contents of EPROMs are verified byte by byte against
the recording on the magnetic tape. In case of error, the defective
EPROM chip is indicated by flashing the corresponding color in the
test image (
0-7
);
— D to load the operating system from floppy disk.
After selecting the source of the operating system to be loaded from the
keyboard, the
RAM
area between
8000H
and
FFFFH
is set up accordingly, bit 6 of
the output port
FEH
is set to
0
or 1 according to the configuration chosen
(
BASIC
or
CP/M
respectively) and bit 7 of the R register is brought back to “
0
”.
The memory configuration will change after the microprocessor fetched the
code for the
JP (HL)
instruction from the old configuration.
The map of the memory in these 3 configurations is shown in Fig. 4.
10
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 ...
