Documentation

I have put here together copies of some documents pertaining to the original CoBra project.

Aside from that, some documents about the particular case of my activity building this computer, back in the day (1990-1996). More precisely, during that time I built two CoBra mainboards and their floppy disk interfaces. The first one I built was grey (no solder mask applied, the bare board only has the tracks solder-coated). Afterwards I built the second board, which is green due to the solder mask applied from the factory. From here on I will refer to them as "the grey mainboard" and "the green mainboard".

The grey mainboard

The green mainboard


All these together are the documents I started this project from, at the end of 2009, and which are the basis of all subsequent developments.

Aside from all the above, I have also included here a section with documents useful in the study of this computer (though some have no connection with it, but might possibly interest the hobbyists), like datasheets for various integrated circuits (TTL, memories, the Z80 CPU and peripherals, OEM documentation about CP/M and so forth. This section will be updated as I find or scan new documents.

1. Original documents (old):

The two images of the ORIGINAL mainboard, along with the ORIGINAL hardware manual scanned are basically the most important starting points, which allowed me to begin this project with high chances of success. Therefore I will take this opportunity to give a very special thanks to Roelof Koning from Holland for these critical pieces of information. I asked him to scan - especially for me - the copy of the original hardware manual he owns, grayscale at 300 dpi. This allowed me a full reproduction of all information in it. Without these two pieces of information I don't think I could have easily get to what you can see today on this website.

In order to get to a correct conclusion by logical means, I decided to follow a double path: followed by a result comparison. So: After all this I did a comparison between the connection lists resulted from these two processes.

Then I analyzed all the modifications visible on both my old mainboards I had built back in the '90s.

The result of all this was the list of mainboard modifications shown here and the FUNCTIONAL version of the original CoBra project (Version 0). This entire process took about two and a half years, during which I also had to keep a job to make a living and I also was fortunate enough to run into some serious health issues.

2. Documents pertaining to and resulted from the analysis of a CoBra mainboard I have assembled back in the '90s:

3. Various schematics and notes copied from or given by various people in the '90s (scanned):

4. Documents re-edited by me in a decent format:

5. Other documents not directly related to CoBra:



1. Original documents:



The original CoBra mainboard printed circuit (dual layer), courtesy of Roelof Koning

Component side, seen from the components:

The bottom (opposite side), seen from the bottom:



The original CoBra hardware manual scanned,
courtesy of Roelof Koning

The original CoBra CP/M manual - photocopy

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"Introducing CoBra"

"OPUS User Manual"

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2. Documents pertaining to and resulted from the analysis of a CoBra mainboard I assembled back in the '90s:



Next, two graphic maps with modifications (one map for each side of the original mainboard printed circuit) and a list of these modifications (cuts and rewirings) resulted from the analysis of the green mainboard I had built in 1991-93 featuring the 80KB RAM modification, the 80 char/line CP/M modification, R/W access in the Basic RAM area for a Basic with a NMI routine, button added for reset to the startup config (COBRA RESET) and NMI button. These two maps contain a graphic image of all track cuts and rewirings explained in the list. Please note these modifications worked in conjunction with two little extra modules containing the 80KB RAM modification and the 80 char/line CP/M modification plus a few more little improvements. The schematics for these modules as well as the printed circuits are shown after the list of modifications, they were connected by wires to various points on the mainboard, according to the labels on the printed circuits.

Mainboard modifications, side 1 (component side):

Mainboard modifications, side 2 (bottom side):



List of connection changes for the original mainboard:

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Schematics for the two extra modules:

These are two little circuits built by me and attached to the mainboard by wires, containing basically the 80KB RAM modification, the 80 char/line CP/M modification, a NMI signal generator controlled by a push button, and a few more little improvements. Please note this is about the particular case of my own constructive solution with the lousy means I had at the time. Not exactly a high-end piece of work (actually crappy in my opinion) but that's what I could do at that moment.

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Module #1 printed circuit:

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Module #2 printed circuit:

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3. Miscellaneous schematics and notes acquired from various people at that time (scanned):



The 64K modification:

The 80K modification:



The 80 char/line CP/M modification:


in the upper right corner there's the initial idea of this circuit (1 switch + 6 diodes) which was given to me by somebody else. Next dowb there's an implementation using two switches and AND gates, at the very bottom there's the final implementation, software activated through the O5 signal (bit 5 of output port FEh). This modification requires a modified CP/M system.

Memory map for the 80K RAM configuration (the 80K RAM modification):



Pinouts for a few integrated circuits:

PAL coder using TTL circuits:





4. Documents re-edited by me in a decent format:



NOTA: The Basic and CP/M manuals are for now not translated yet, and the hardware manual is still missing pages 64-70 with component placement on the power source printed circuit board, the RGB monitor interface and component placement on the mainboard. These things are still on my to-do list, and I will do them too when I find the time.

The original CoBra hardware manual

The original CoBra Basic manual (not translated to English yet)

The original CP/M CoBra manual (not translated to English yet)



5.1 7400 Series TTL Datasheets:



7400Quadruple 2-input positive-NAND gates
7402Quadruple 2-input positive-NOR gates
7403Quadruple 2-input positive-NAND gates with open-collector outputs
7404Hex inverters
7405Hex inverters with open-collector outputs
7406Hex inverter buffers/drivers with open-collector high-voltage outputs
7407Hex buffers/drivers with open-collector high-voltage outputs
7408Quadruple 2-input positive-AND gates
7409Quadruple 2-input positive-AND gates with open-collector outputs
7410Triple 3-input positive-NAND gates
7411Triple 3-input positive-AND gates
7412Triple 3-input positive-NAND gates with open-collector outputs
7413Dual 4-input positive-NAND Schmitt triggers
7414Hex Schmitt-trigger inverters
7415Triple 3-input positive-AND gates with open-collector outputs
7416Hex inverter buffers/drivers with open-collector high-voltage outputs (15V)
7417Hex buffers/drivers with open-collector high-voltage outputs (15V)
7419Schmitt-trigger positive-NAND gates and inverters with totem-pole outputs
7420Dual 4-input positive-NAND gates
7421Dual 4-input positive-AND gates
7424Schmitt-trigger positive-NAND gates and inverters with totem-pole outputs
7426Quadruple 2-input high-voltage interface positive-NAND gates
7427Triple 3-input positive-NOR gates
74308-input positive-NAND gate
7431Delay elements
7432Quadruple 2-input positive-OR gates
7433Quadruple 2-input positive-NOR buffers with open-collector outputs
7437Quadruple 2-input positive-NAND buffers
7438Quadruple 2-input positive-NAND buffers with open-collector outputs
74424-line BCD to 10-line decimal decoders
7446BCD-to-seven-segment decoders/drivers with open collector outputs
7447BCD-to-seven-segment decoders/drivers with open collector outputs
7448BCD-to-seven-segment decoders/drivers with internal pull-ups
7449BCD-to-seven-segment decoders/drivers with open collector outputs and blanking input
7451AND-OR-INVERT gates
7473Dual J-K flip-flops with CLEAR
7474Dual D-type positive-edge-triggered flip-flops with PRESET and CLEAR
74754-bit bistable latches
74774-bit bistable latches
74854-bit magnitude comparators
7486Quadruple 2-input Exclusive-OR gates
7490Decade counters
7492Divide-by-twelve counters
74934-bit binary counters
74954-bit parallel access shift registers
74107Dual J-K flip-flops with CLEAR
74109Dual J-K positive-edge-triggered flip-flops with PRESET and CLEAR
74112Dual J-K negative-edge-triggered flip-flops with PRESET and CLEAR
74122Retriggerable monostable multivibrators
74123Retriggerable monostable multivibrators
74125Quadruple bus buffers with 3-state outputs and ENABLE inputs
74126Quadruple bus buffers with 3-state outputs and ENABLE inputs
74130Retriggerable monostable multivibrators
74132Quadruple 2-input positive-NAND Schmitt triggers
74136Quadruple 2-input Exclusive-OR gates with open-collector outputs
741383-line to 8-line decoders/demultiplexers
74139Dual 2-line to 4-line decoders/demultipliers
74145BCD-to-decimal decoders/drivers
7414710-line decimal to 4-line BCD priority encoder
741488-line to 3-line binary (octal) priority encoder
7415016 to 1 selector/multiplexer
741518 to 1 selector/multiplexer
74153Dual 4-line to 1-line data selector/multiplexer
74155Dual 2-line to 4-line decoder/demultiplexer
74156Dual 2-line to 4-line decoder/demultiplexer with open-collector outputs
74157Quadruple 2-line to 1-line data selectors/multiplexers
74158Quadruple 2-line to 1-line data selectors/multiplexers with inverted outputs
74160Synchronous 4-bit decade counter with asynchronous CLEAR input
74161Synchronous 4-bit binary counter with asynchronous CLEAR input
74162Synchronous 4-bit decade counter with synchronous CLEAR input
74163Synchronous 4-bit binary counter with synchronous CLEAR input
741648-bit serial-in parallel-out shift register
741658-bit parallel-in serial-out shift register
741668-bit parallel/serial-in serial-out shift register
74169Synchronous 4-bit up/down binary counter
741734-bit D-type register with 3-state outputs
74174Hex D-type flip-flops with asynchronous CLEAR
74175Quadruple D-type flip-flops with asynchronous CLEAR and complementary outputs
74181Arithmetic logic unit/function generator
74190Synchronous BCD up/down counter
74191Synchronous binary up/down counter
74192Synchronous BCD up/down counter (dual clock with CLEAR)
74193Synchronous binary up/down counter (dual clock with CLEAR)
741944-bit bidirectional universal shift register
742212 monostabili/multivibratori cu intrari TRIGGER-SCHMITT
742408 buffere si drivere de linie cu iesiri tri-state
742418 buffere si drivere de linie cu iesiri tri-state
742434 transceivere de magistrala, asincrone bidirectionale
742448 buffere si drivere de linie cu iesiri tri-state
742458 transceivere de magistrala, asincrone bidirectionale cu iesiri tri-state
74246Decodor/driver de la BCD la sapte segmente cu iesiri cu colector in gol (30V)
74247Decodor/driver de la BCD la sapte segmente cu iesiri cu colector in gol (15V)
74248Decodor/driver de la BCD la sapte segmente cu iesiri cu colector in gol si rezistori pullup interni (5.5V)
74251Multiplexor 8:1 cu iesiri tri-state
742532 multiplexoare 4:1 cu iesiri tri-state
742574 multiplexoare 2:1 cu iesiri tri-state
742584 multiplexoare 2:1 cu iesiri tri-state negate
74259Latch adresabil pe 8 biti
742664 porti SAU-EXCLUSIV-NU cu iesiri cu colector in gol
742738 bistabili tip D cu stergere asincrona
742794 latch-uri S-R
74280Generator/verificator de paritate pe 9 biti
74283Sumator pe 4 biti cu bit de carry rapid
74290Numarator decadic pe 4 biti
74292Divizor programabil de frecventa / cronometru digital
74293Numarator pe 4 biti
74294Divizor programabil de frecventa / cronometru digital
74295Registru de deplasare stinga/dreapta pe 4 biti cu iesiri tri-state
742984 multiplexoare 2:1 cu stocare
74299Registru universal de deplasare/stocare pe 8 biti cu iesiri tri-state si stergere asincrona
74348Codor cu prioritate de la 8 la 3 linii cu iesiri tri-state
743656 drivere de magistrala cu iesiri tri-state
743666 drivere de magistrala cu iesiri tri-state negate
743676 drivere de magistrala cu iesiri tri-state
743686 drivere de magistrala cu iesiri tri-state negate
743738 latch-uri tip D transparente cu iesiri tri-state
743748 bistabili tip D cu actionare pe front si iesiri tri-state
74375Latch bistabil pe 4 biti
743778 bistabili cu cite o singura iesire
743786 bistabili cu cite o singura iesire
743794 bistabili cu cite doua iesiri (complementare)
743902 numaratoare decadice
743932 numaratoare pe 4 biti
743994 multiplexoare 2:1 cu stocare
74422Monostabil multivibrator retriggerabil cu rezistor de temporizare intern
74423Monostabil multivibrator retriggerabil
744404 transceivere de magistrala tridirectionale cu iesiri cu colector in gol
744414 transceivere de magistrala tridirectionale cu iesiri cu colector in gol negate
744424 transceivere de magistrala tridirectionale cu iesiri tri-state
744444 transceivere de magistrala tridirectionale cu iesiri tri-state adevarate si negate
744658 buffere cu iesiri tri-state cu validare comuna
744668 buffere cu iesiri tri-state cu validare comuna si iesiri negate
744678 buffere cu iesiri tri-state cu validari separate pe grupuri de 4
744688 buffere cu iesiri tri-state cu validari separate pe grupuri de 4 si iesiri negate
745408 buffere si drivere de linie cu iesiri tri-state negate
745418 buffere si drivere de linie cu iesiri tri-state
74592Numarator binar pe 8 biti cu registru de intrare paralel
74593Numarator binar pe 8 biti cu registru de intrare paralel si intrari/iesiri tri-state
74594Registru de deplasare pe 8 biti cu latch buffer la iesire
74595Registru de deplasare pe 8 biti cu latch tri-state la iesire
74596Registru de deplasare pe 8 biti cu latch cu colector in gol la iesire
74597Registru de deplasare pe 8 biti cu latch la intrare
74598Registru de deplasare pe 8 biti cu latch la intrare si intrari/iesiri tri-state
74599Registru de deplasare pe 8 biti cu latch la iesire si iesiri cu colector in gol
746208 transceivere de magistrala bidirectionale cu iesiri tri-state negate
746218 transceivere de magistrala bidirectionale cu iesiri cu colector in gol
746238 transceivere de magistrala bidirectionale cu iesiri tri-state
746408 transceivere de magistrala bidirectionale cu iesiri tri-state negate
746418 transceivere de magistrala bidirectionale cu iesiri cu colector in gol
746428 transceivere de magistrala bidirectionale cu iesiri cu colector in gol negate
746448 transceivere de magistrala bidirectionale cu iesiri cu colector in gol adevarate si negate
746458 transceivere de magistrala bidirectionale cu iesiri tri-state
746468 transceivere si registre de magistrala cu iesiri tri-state
746478 transceivere si registre de magistrala cu iesiri cu colector in gol
746488 transceivere si registre de magistrala cu iesiri tri-state negate
746498 transceivere si registre de magistrala cu iesiri cu colector in gol negate
746518 transceivere si registre de magistrala cu iesiri tri-state negate
746528 transceivere si registre de magistrala cu iesiri tri-state
746538 transceivere si registre de magistrala cu iesiri negate tri-state si cu colector in gol
74668Numarator bidirectional sincron pe 4 biti decadic
74669Numarator bidirectional sincron pe 4 biti
746704 registri de cite 4 biti cu iesiri tri-state
74673Registru de deplasare pe 16 biti cu intrare/iesire seriala si registru de stocare cu iesiri paralele
74674Registru de deplasare pe 16 biti cu intrari paralele si iesire seriala
74682Comparator de egalitate cu magnitudine de 8 biti cu rezistori pullup de 20 kΩ la iesiri
74684Comparator de egalitate cu magnitudine de 8 biti
74685Comparator de egalitate cu magnitudine de 8 biti cu iesiri cu colector in gol
74686Comparator de egalitate cu magnitudine de 8 biti cu output enable
74687Comparator de egalitate cu magnitudine de 8 biti cu output enable si iesiri cu colector in gol
74688Comparator de egalitate cu magnitudine de 8 biti cu output enable
74696Numarator decadic bidirectional sincron cu registru de iesire si iesiri tri-state multiplexate, cu stergere asincrona
74697Numarator binar bidirectional sincron cu registru de iesire si iesiri tri-state multiplexate, cu stergere asincrona
74699Numarator binar bidirectional sincron cu registru de iesire si iesiri tri-state multiplexate, cu stergere sincrona


5.2 Russian TTL equivalents:



The Soviet Union started manufacturing TTL ICs with 7400 series pin-out in late 1960s and early 1970s. Part numbering is different from the Western series.
The function of the unit is described with the suffix, according to the table below:

American code Russian suffix American code Russian suffix
7400 ЛА3 74140 ЛА6
7401 ЛА8 74141 ИД1
7402 ЛЕ1 74145 ИД10
7403 ЛА9 74148 ИВ1
7404 ЛН1 74150 КП1
7405 ЛН2 74151 КП7
7406 ЛН3 74152 КП5
7407 ЛН4 74153 КП2
7408 ЛИ1 74154 ИД3
7410 ЛА4 74155 ИД4
7411 ЛИ3 74160 ИЕ9
7412 ЛА10 74163 ИЕ10
7413 ТЛ1 74164 ИР8
7414 ТЛ2 74165 ИР9
7415 ЛИ4 74168 ИЕ16
7416 ЛН5 74169 ИЕ17
7417 ЛП4 74170 РП1
7420 ЛА1 74172 РП3
7421 ЛИ6 74173 ИР15
7422 ЛА7 74174 ТМ9
7423 ЛЕ2 74175 ТМ8
7425 ЛЕ3 74180 ИП2
7426 ЛА11 74181 ИП3
7427 ЛЕ4 74182 ИП4
7428 ЛЕ5 74184 ПР6
7430 ЛА2 74185 ПР7
7432 ЛЛ1 74192 ИЕ6
7434 ЛИ9 74193 ИЕ7
7437 ЛА12 74194 ИР11
7438 ЛА13 74195 ИР12
7440 ЛА6 74196 ИЕ14
7442 ИД6 74197 ИЕ15
7450 ЛР1 74198 ИР13
7451 ЛР11 74240 АП3
7453 ЛР3 74241 АП4
7454 ЛР13 74242 ИП6
7455 ЛР4 74243 ИП7
7460 ЛД1 74245 АП6
7464 ЛР9 74251 КП15
7465 ЛР10 74253 КП12
7472 ТВ1 74257 КП11
7474 ТМ2 74258 КП14
7475 ТМ7 74260 ЛЕ7
7477 ТМ5 74261 ИП8
7480 ИМ1 74279 ТР2
7481 РУ1 74283 ИМ6
7482 ИМ2 74295 ИР16
7483 ИМ3 74298 КП13
7485 СП1 74299 ИР24
7490 ИЕ2 74322 ИР28
7492 ИЕ4 74358 ИМ7
7493 ИЕ5 74366 ЛН6
7497 ИЕ8 74367 ЛП11
74107 ТВ6 74373 ИР22
74109 ТВ15 74374 ИР23
74112 ТВ9 74377 ИР27
74113 ТВ10 74381 ИК2
74114 ТВ11 74384 ИП9
74121 АГ1 74385 ИМ7
74123 АГ3 74395 ИР25
74124 ГГ1 74482 ВГ1
74125 ЛП8 74630 ВЖ1
74128 ЛЕ6 74670 ИР26
74132 ТЛ3 AM25S05 ИК1
74134 ЛА19 AM25S07 ИР18
74136 ЛЛ3 AM25S08 ИР19
74138 ИД7 AM25S09 ИР20
74139 ИД14 AM25S10 ИР21