Editing Commodore Datasette

{{Short description|Dedicated magnetic tape data storage device}}
[[file:Commodore-Datasette-C2N-Mk1-Front.jpg|thumb|The third, most common version of the 1530 C2N Datassette]]

The '''Commodore 1530''' ('''C2N''') '''Datasette''', later also '''Datassette''' (a [[portmanteau]] of ''[[data]]'' and ''cassette''), is [[Commodore International|Commodore]]'s dedicated [[magnetic-tape data storage]] device. Using [[Cassette tape#data|compact cassettes]] as the [[storage medium]], it provides inexpensive storage to Commodore's [[8-bit]] computers, including the [[Commodore PET|PET]], [[VIC-20]], and [[Commodore 64]]. A physically similar model, '''Commodore 1531''', was made for the [[Commodore 16]] and [[Commodore Plus/4|Plus/4]] series computers.

== Features ==
[[File:Commodore-Datasette-C2N-Mk2-Back.jpg|thumb|The connection cable to the Datasette]]

The Datasette is probably the most sophisticated tape-storage method of any microcomputer.{{r|deceukelaire198502}} Typical [[cassette tape|compact cassette]] interfaces of the late 1970s use a small controller in the computer to convert [[digital data]] to and from [[analog audio]] tones. The interface connects to the cassette deck using normal audio cables like [[RCA connector|RCA jacks]] or [[phone connector (audio)|3.5mm phone jacks]]. Such a system is compatible with the [[Apple II]]<ref>{{cite magazine | magazine = Apple Orchard | title = The Apple II Cassette Interface | url = https://archive.org/details/Apple-Orchard-v2n1-1981-Spring/page/n57 | page = 57-58 | publisher = International Apple Core | volume = 2 | issue = 1 | date = Spring 1981 | issn = 0277-1950 | oclc = 647837472 | via = [[Internet Archive]] | df = dmy-all}}</ref>{{rp|pages=[https://archive.org/details/Apple-Orchard-v2n1-1981-Spring/page/n57 57-58]}} and [[TRS-80 Color Computer]], as well as many [[S-100 bus]] systems, and allows them to be used with any cassette player with suitable connections,<ref>{{cite magazine |magazine= Popular Mechanics |date=February 1983 |title=The Five Friendliest Computers |first=Herb |last=Friedman |pages=97}}</ref> but using analog tones—similar to how [[dial-up modem]]s work—often results in [[read error]]s instead of successful loading of data.{{r|deceukelaire198502}}

[[file:Commodore Basic screenshot.jpg|thumb|left|The Datasette loading process]]

In the Datasette, instead of writing two tones to tape to indicate bits, patterns of [[Square wave (waveform)|square wave]]s are used, including a [[parity bit]]. Programs are written twice to tape for [[error detection and correction|error correction]]; if an error is detected when reading the first recording, the computer corrects it with data from the second.{{r|deceukelaire198502}} The Datasette has built-in [[analog-to-digital converter]]s and [[audio filter]]s to convert the computer's digital data into analog audio and vice versa. Connection to the computer is done via a proprietary [[edge connector]] (Commodore 1530) or [[mini-DIN connector]] (1531). The absence of recordable audio signals on this interface makes the Datasette and clones the only cassette recorders usable with Commodore computers, until aftermarket converters made the use of ordinary recorders possible.

Because of its digital format the Datasette is both more reliable than other data cassette systems and very slow,<ref name="deceukelaire198502">{{cite news | url=http://www.atarimagazines.com/compute/issue57/turbotape.html | title=How TurboTape Works | work=Compute! | date=February 1985 | access-date=30 October 2013 | author=De Ceukelaire, Harrie | pages=112}}</ref><ref name="128book">{{cite book | chapter-url=https://archive.org/stream/The_Official_Book_for_the_Commodore_128#page/n21/mode/2up | title=The Official Book for the Commodore 128 Personal Computer | publisher=Howard W. Sams & Co. | author1=Waite, Mitchell | author2=Lafore, Robert | author3=Volpe, Jerry | year=1985 | pages=11–32 | isbn=0-672-22456-9 | chapter=Peripherals: Displays, Disk Drives, Printers, and More}}</ref> transferring data at around {{nowrap|50 bytes}} per second. After the Datasette's launch, however, special ''[[turbo tape]]'' software appeared, providing much faster loading and saving.{{r|deceukelaire198502}} Such software was integrated into most commercial prerecorded applications (mostly games), as well as being available separately for loading and saving the users' homemade programs and data. These programs were only widely used in Europe, as the US market had long since moved onto disks.

Datasettes can typically store about {{nowrap|100 [[kilobyte|kByte]]}} per {{nowrap|30 minute}} side.<ref>{{Cite web|url=http://starbase.globalpc.net/~vanessa/hobbies/commodore-info.html|title=Basic Commodore information}}{{dead link|date=June 2017 |bot=Jennica |fix-attempted=yes }}</ref> The use of ''turbo tape'' and other fast loaders increased this number to roughly {{nowrap|1000 kByte}}.

The Datasette has only one connection cable, with a {{convert|0.156|in|adj=on}}&ndash;spacing<ref>{{cite magazine|title=Rupert Report: Computers in Control|magazine=Ahoy!|date=July 1987|page=32|last=Rupert|first=Dale|issn=8750-4383|publisher=Ion International|location=New York|url=https://archive.org/stream/ahoy-magazine-43/Ahoy_43_July_1987#page/n35/mode/2up|access-date=2018-04-12}}</ref> PCB [[edge connector]] at the computer end. All input/output signals to the Datasette are all digital, and so all [[digital-to-analog conversion]], and vice versa, is handled within the unit. Power is also included in this cable. The [[pinout]] is ground, {{nowrap|+5 V [[direct current|DC]]}}, motor, read, write, key-sense.<ref>[http://old.pinouts.ru/Storage/CassetteC64_pinout.shtml pinouts.ru - C64 Cassette pinout], 2012-01-15</ref> The sense signal monitors the play, rewind, and fast-forward buttons but cannot differentiate between them. A mechanical interlock prevents any two of them from being pressed at the same time. The motor power is derived from the computer's unregulated {{nowrap|9 V DC}} supply<ref>{{cite book|title=Commodore 64 Programmer's Reference Guide|year=1984|isbn=0-672-22056-3|publisher=Commodore Business Machines|location=West Chester|at=Commodore 64 Schematic Diagram|url=http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/C64SchematicP2.png|access-date=2018-04-12}}</ref> via a transistor circuit.<ref>{{cite book|title=SAMS Computerfacts CC4: Computer: Commodore 64|page=2|year=1984|publisher=Howard W. Sams|location=Indianapolis}}</ref><!-- Sams says it measures 6.45V under load (p. 9). -->

== Encoding ==
[[File:Commodore-Datasette-C2N-Mk1-Open-Back.jpg|thumb|Inside the Datasette]]
[[File:c2n waveform.png|thumb|left|The resulting waveform from storing data]]
{{Listen|filename=Datasette.ogg|title=Datasette sound sample|description=Commodore Datasette 18-second sound sample|format=[[Ogg]]}}

To record physical data, the [[zero-crossing]] from positive to negative voltage of the analog signal is measured. The resulting time between these positive to negative crossings is then compared to a threshold to determine whether the time since the last crossing is short (0) or long (1).<ref name="wav-prg_sf-tape">{{cite web|title=How Commodore tapes work|url=http://wav-prg.sourceforge.net/tape.html}} 091205 wav-prg.sourceforge.net</ref> Note the lower amplitude for the shorter periods.

A circuit in the tape unit transforms the analog signal into a logical 1 or 0, which is then transmitted to the computer via the [[Commodore 64#Input/output (I/O) ports and power supply|tape connector]]. Inside the computer, the first [[MOS Technology CIA|Complex Interface Adapter]] (6526) in the C64 senses when the signal goes from one to zero. This event is called trigger and causes an [[interrupt request]]. This event can be handled by a handler code, or simply discovered by testing bit 4 of location $DC0D. The points that trigger this event are indicated by the black circles in the figure.<ref name="wav-prg_sf-tape" />

Inside the tape device the [[tape head|read head]] signal is fed into an [[operational amplifier]] (1) whose output signal is [[direct current|DC]]-filtered. Op-amp (2) amplifies and feeds an RC filter. Op-amp (3) amplifies the signal again followed by another DC filter. Op-amp (4) amplifies the signal into [[clipping (signal processing)|clipping]] the [[sine wave|sine]]-formed signal. The positive and negative rails for all op-amps are wired to +5V DC and [[Ground (electricity)|GND]]. The clipped signal therefore fits into the [[transistor–transistor logic|TTL]] electrical level window of the [[Schmitt trigger]] step that in turn feeds the digital cassette port.<ref name="c2n_schematic">Datasette service manual model C2N/1530/1531, preliminary, Oct. 1984 PN-314002-02</ref>

On the [[PAL]] version of the C64, the time granularity is {{nowrap|1.014 [[microsecond|μs]]}} (for NTSC {{nowrap|0.978 μs}}). Since each bit uses {{nowrap|3284 [[Clock signal|clock cycles]]}} this means {{nowrap|3284 * 1.014 μs}} = {{nowrap|3330 μs/bit.}} or a {{nowrap|300 bit/s}} data rate.

Once the bits can be decoded, they are fed into a [[shift register]]<!--MSB or LSB first?--> and are continuously compared to a special bit sequence. This bit sequence can also be seen as a byte. A bit-sequence match means that the stream is byte-synchronized. The first byte to compare with is called the ''lead-in byte''. If matched, it's compared to the ''sync byte'' as well.<ref name="wav-prg_sf-tape" />

An example: Turbo Tape 64 has a ''lead-in byte'' $02 (binary 00000010), ''sync byte'' $09 (binary 00001001) and a following sync sequence of $08, $07, $06, $05, $04, $03, $02, $01.<ref name="deceukelaire198502" /><ref name="wav-prg_sf-tape" />

== Models ==
[[file:Datasette c2n.jpg|thumb|upright|The C2N Cassette Unit, the original Datasette model shape]]
[[file:Datassette 1531.jpg|thumb|Datassette 1531]]

=== PET, VIC-20, C64/128 ===

There are at least four main models of the 1530/C2N Datassette:

* The original modified [[Sanyo]] M1540A cassette drive, built into the earliest models of PET in 1977. This was a standard shoebox tape recorder with a corner of the case removed and modified electronics; a Commodore PCB was installed internally in place of the Sanyo electronics. To disguise the Sanyo brand, Commodore simply fitted a Commodore badge over the original logo.<ref>{{Cite web |last=Zimmerman |first=Bo |title=cbm-trivia-13.txt |url=https://www.zimmers.net/anonftp/pub/cbm/faq/trivia/cbm-trivia-13.txt}}</ref>
* The second built-in Datassette in the PET 2001: another standard consumer model (sold in some markets as CCE CCT1020) modified with a Commodore PCB. Black cassette lid, five white keys, no tape counter, no SAVE [[light-emitting diode|LED]]<ref>{{cite web|url=https://books.google.com/books?id=Be5xZ1ovVx8C&q=transicorder+ct+1020&pg=PA11|title=Placar Magazine|first=Editora|last=Abril|date=26 October 1973|publisher=Editora Abril|access-date=27 June 2017|via=Google Books}}</ref>
* Black body original-shape model, black cassette lid, five black keys, no tape counter, no SAVE LED
* White body original-shape model, black cassette lid, five black keys, with tape counter, no SAVE LED
* White body new-shape model, silver cassette lid, six black keys, with white tape counter SAVE LED on left side
* White body new-shape model, silver cassette lid, six black keys, with tape counter and a red SAVE LED on the right
* As above but with black pattern and silvery Commodore logo, six black keys, tape counter and a red SAVE LED on right side

The first two external models were made as PET peripherals, and styled after the PET 2001 built-in tape drive. The latter two were styled and marketed for the VIC-20 and C64. All 1530s are compatible with all those computers, as well as the [[Commodore 128|C128]].

In addition to this, some models came with a small hole above the keys, to allow access to the adjustment screw of the tape head [[azimuth#Other uses of the word|azimuth]] position. A small [[screwdriver]] can thus easily be used to affect the adjustment without disassembling the Datassette's chassis.

Confusingly, the Datassette at various times was sold both as the ''C2N DATASETTE UNIT Model 1530'' and as the ''1530 DATASSETTE UNIT Model C2N''. Note the difference in spelling (one ''S'' versus two) used on the original product packaging.<ref>{{cite web|url=http://www.zimmers.net/cbmpics/dtapes.html|title=Commodore Datasettes|author=Bo Zimmerman|work=Commodore Gallery|access-date=20 April 2012}}</ref>

Like Datasette models, the recording format is compatible across computers; the VIC, for example, can read PET cassettes.<ref name="thornburg198104">{{Cite magazine |last=Thornburg |first=David D. |date=April 1981 |title=The Commodore VIC-20: A First Look |url=http://www.atarimagazines.com/compute/issue11/12_1_THE_COMMODORE_VIC-20_A_FIRST_LOOK.php |magazine=Compute! |page=26}}</ref><ref name="butterfield198104">{{Cite magazine |last=Butterfield |first=JIm |author-link=Jim Butterfield |date=April 1981 |title=Advice to PET Owners: How To Be A VIC Expert |url=http://www.atarimagazines.com/compute/issue11/17_1_ADVICE_TO_PET_OWNERS_HOW_TO_BE_A_VIC_EXPERT.php |magazine=Compute! |issue=11 |page=34}}</ref>

=== C16/116 and Plus/4 ===

Similar in physical appearance to the 1530/C2N models is the '''Commodore 1531''', made for the [[Commodore 16]] and [[Commodore Plus/4|Plus/4]] series computers. This has a [[Mini-DIN connector]] in place of the PCB edge connector. This can be used with a C64/128 via an adaptor, which was supplied by Commodore with some units.

*Black/charcoal body new shape model, silver cassette lid, six light gray keys, with tape counter and a red SAVE LED

== Popularity ==
[[file:Datassette clone.jpg|thumb|One of the few clones, a Phonemark model 4403]]

The Datasette was more popular outside than inside the United States. [[U.S. Gold]], which imported American computer games to Britain, often had to wait until they were converted from disk because most British Commodore 64 owners used tape,<ref name="anderson198506">{{cite news | url=https://archive.org/stream/zzap64-magazine-002/ZZap_64_Issue_002_1985_Jun#page/n45/mode/2up | title=On top of the US Goldmine | work=Zzap!64 | date=June 1985 | access-date=26 October 2013 | author=Anderson, Chris | pages=46–48 | type=interview}}</ref><ref name="pountain198501">{{cite news | url=https://archive.org/details/BYTE_Vol_10-01_1985-01_Through_The_Hourglass | title=The Amstrad CPC 464 | work=BYTE | date=January 1985 | access-date=27 October 2013 | author=Pountain, Dick | pages=[https://archive.org/details/BYTE_Vol_10-01_1985-01_Through_The_Hourglass/page/n402 401]}}</ref> while the US magazine ''[[Compute!'s Gazette]]'' reported that by 1983 "90 percent of new Commodore 64 owners bought a disk drive with their computer".<ref name="halfhill198312">{{cite news | url=https://archive.org/stream/1983-12-computegazette/Compute_Gazette_Issue_06_1983_Dec#page/n7/mode/2up | title=The Editor's Notes | work=Compute!'s Gazette | date=Dec 1983 | access-date=6 February 2016 | author=Halfhill, Tom | pages=6 | type=editorial}}</ref> ''[[Computer Gaming World]]'' reported in 1986 that British cassette-based software had failed in the United States because "97% of the Commodore systems in the USA have disk drives";<ref name="wagner198608">{{cite magazine | title=The Commodore Key | magazine=Computer Gaming World | date=August 1986 | url=http://www.cgwmuseum.org/galleries/index.php?year=1986&pub=2&id=30 | access-date=1 November 2013 | author=Wagner, Roy | pages=28}}</ref> by contrast, [[MicroProse]] reported in 1987 that 80% of its 100,000 sales of ''[[Gunship (video game)|Gunship]]'' in the UK were on cassette.<ref name="brooks198711">{{cite magazine | title=Titans of the Computer Gaming World / MicroProse | magazine=Computer Gaming World | date=November 1987 | url=http://www.cgwmuseum.org/galleries/index.php?year=1987&pub=2&id=41 | access-date=2 November 2013 | author=Brooks, M. Evan | pages=16}}</ref> In the United States disk drives quickly became standard, despite the 1541 costing roughly five times as much as a Datasette. In most parts of Europe, the Datasette was the medium of choice for several years after its launch, although floppy disk drives were generally available. The inexpensive and widely available audio cassettes made the Datasette a good choice for the budget-aware home computer mass market.

== See also ==

* [[Famicom Data Recorder]]
* [[Fast loader]]
* [[IBM cassette tape]]
* [[Kansas City standard]]
* [[Magnetic-tape data storage]]

== References ==

{{reflist}}

== External links ==

* [https://web.archive.org/web/20060623113910/http://www.xs4all.nl/~lagendr/Menu/DATS.htm Similar Commodore tape drives]
* [http://www.zimmers.net/cbmpics/dtapes.html Datasette photos]
* [http://www.zimmers.net/anonftp/pub/cbm/crossplatform/transfer/C2N232/ Description of tape format with conversion utilities and code]
* [http://www.ktverkko.fi/~msmakela/8bit/c2n232/index.en.html C2N232 project] to build a hardware adaptor/software program to archive Commodore Datasette files to a modern computer.
* [http://www.luigidifraia.com/c64/dc2n/index.html DC2N Homepage] {{Webarchive|url=https://web.archive.org/web/20190617084318/https://www.luigidifraia.com/c64/dc2n/index.html |date=2019-06-17 }} Digital C2N replacement project.
* [https://3dwarehouse.sketchup.com/model/190d61f2e39c17bbd51f7d3e5267fbfb/Commodore-Datasette-1530 Sketchup model of the Commodore Datasette 1530.] Sketchup model of the Commodore Datasette 1530.

{{Magnetic tape data formats}}

[[Category:CBM storage devices]]
[[Category:Home computer peripherals]]
[[Category:Commodore 64]]
[[Category:VIC-20]]
[[Category:Tape-based computer storage]]