Datassette
Encyclopedia
The Commodore 1530 Datasette (a portmanteau of data
and cassette), was Commodore
's dedicated computer tape drive
.
It provided access to an inexpensive storage medium for Commodore's 8-bit
home/personal computer
s, notably the PET
, VIC-20
, and C64
. A physically similar model Commodore 1531 was made for the Commodore 16
and Plus/4
series computers.
s to convert the computer's digital
information into analog sound and vice versa (much like a modem
does over a telephone line). Connection to the computer was done via a proprietary edge connector
(Commodore 1530) or mini-DIN connector
(Commodore 1531). The absence of recordable audio signals on this interface made the Datasette and its few clones the only cassette recorders usable with CBM's machines, until aftermarket converters made the use of ordinary recorders possible.
The inexpensive and widely available audio cassettes made the Datasette a good choice for the budget-aware home computer mass market. 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. In the United States
, however, disk drives quickly became standard, despite the Commodore 1541
floppy drive costing roughly 5 times as much as a Datasette.
The Datasette was very slow albeit extremely reliable, transferring data at around 50 bytes per second, and even the 1541 was significantly faster. Some years after the Datasette's launch, however, special turbo tape
software appeared, providing much faster tape operation (loading and saving). 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 could typically store about 100 kByte per 30 minute side. The use of turbo tape and other fast loaders increased this number to roughly 1000 kByte.
edge connector at the computer end. All input/output signals to the datasette are all digital and so all digital to analog and vice versa is handled within the unit. Power is also included in this cable. The pinout is ground, +5V, motor, read, write, key-sense. The sense signal monitors the play, rewind, and fast-forward buttons, but cannot differentiate between them. A mechanical interlock prevented any two of them being pressed at the same time. Unregulated is used to power the cassette motor.
A circuit in the tape unit transforms the analog signal into a logical one or zero which is then transmitted to the computer via the tape connector. Inside the computer the first 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.
Inside the tape device the read head
signal is fed into an operational amplifier
(1) whose output signal is 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
the sine formed signal. The positive and negative rails for all op-amps are wired to +5V DC and GND. The clipped signal therefore fits into the TTL electrical level window of the schmitt trigger step that in turn feeds the digital cassette port.
On the PAL
version of the C64, the time granularity is 1.014 µs (for NTSC 0.978 µs). For a 300 bit/s data rate this means 3284 * 1.014 µs per data bit.
Once the bits can be decoded it's fed into a shift register
and compared to a special bit sequence continuously. This bit sequence can also be seen as a byte. A bit sequence match means the stream is byte synchronized. The first byte to compare with is called lead-in byte. If matched, it's compared to the sync byte as well.
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, $03, $02, $01.
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 were compatible with all those computers, as well as the 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 position. A small screwdriver
could 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 versus two s 'es) used on the original product packaging.
and Plus/4
series computers. This had a Mini-DIN connector
in place of the PCB edge connector. This could be used with a C64/128 via an adaptor, which was supplied by Commodore with some units.
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
and cassette), was Commodore
Commodore International
Commodore is the commonly used name for Commodore Business Machines , the U.S.-based home computer manufacturer and electronics manufacturer headquartered in West Chester, Pennsylvania, which also housed Commodore's corporate parent company, Commodore International Limited...
's dedicated computer tape drive
Tape drive
A tape drive is a data storage device that reads and performs digital recording, writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.A tape drive provides...
.
It provided access to an inexpensive storage medium for Commodore's 8-bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
home/personal computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
s, notably the PET
Commodore PET
The Commodore PET was a home/personal computer produced from 1977 by Commodore International...
, VIC-20
Commodore VIC-20
The VIC-20 is an 8-bit home computer which was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the PET...
, and C64
Commodore 64
The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
. A physically similar model Commodore 1531 was made for the Commodore 16
Commodore 16
The Commodore 16 was a home computer made by Commodore with a 6502-compatible 8501 CPU, released in 1984. It was intended to be an entry-level computer to replace the VIC-20 and it often sold for 99 USD...
and Plus/4
Commodore Plus/4
The Commodore Plus/4 was a home computer released by Commodore International in 1984. The "Plus/4" name refers to the four-application ROM resident office suite ; it was billed as "the productivity computer with software built-in"...
series computers.
Description and history
The Datasette contained built-in analog to digital converters and audio filterAudio filter
An audio filter is a frequency dependent amplifier circuit, working in the audio frequency range, 0 Hz to beyond 20 kHz. Many types of filters exist for applications including graphic equalizers, synthesizers, sound effects, CD players and virtual reality systems.Being a frequency dependent...
s to convert the computer's digital
Digital signal
A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...
information into analog sound and vice versa (much like a modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
does over a telephone line). Connection to the computer was done via a proprietary edge connector
Edge connector
An edge connector is the portion of a printed circuit board consisting of traces leading to the edge of the board that are intended to plug into a matching socket. The edge connector is a money-saving device because it only requires a single discrete female connector , and they also tend to be...
(Commodore 1530) or mini-DIN connector
Mini-DIN connector
The mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
(Commodore 1531). The absence of recordable audio signals on this interface made the Datasette and its few clones the only cassette recorders usable with CBM's machines, until aftermarket converters made the use of ordinary recorders possible.
The inexpensive and widely available audio cassettes made the Datasette a good choice for the budget-aware home computer mass market. In most parts of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, the Datasette was the medium of choice for several years after its launch, although floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
drives were generally available. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, however, disk drives quickly became standard, despite the Commodore 1541
Commodore 1541
The Commodore 1541 , made by Commodore International, was the best-known floppy disk drive for the Commodore 64 home computer. The 1541 was a single-sided 170 kilobyte drive for 5¼" disks...
floppy drive costing roughly 5 times as much as a Datasette.
Turbo Tape
Turbo Tape is a fast loader program for the Commodore 64 microcassette drive.The built in routines in C64, for storing and reading data to/from MC-tapes was made for safe storing rather than speed. Better tape-quality in the 1980s made it possible to store data more effectively, reducing...
software appeared, providing much faster tape operation (loading and saving). 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 could typically store about 100 kByte per 30 minute side. The use of turbo tape and other fast loaders increased this number to roughly 1000 kByte.
Interface
The Datasette has only one connection cable with a PCBPrinted circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
edge connector at the computer end. All input/output signals to the datasette are all digital and so all digital to analog and vice versa is handled within the unit. Power is also included in this cable. The pinout is ground, +5V, motor, read, write, key-sense. The sense signal monitors the play, rewind, and fast-forward buttons, but cannot differentiate between them. A mechanical interlock prevented any two of them being pressed at the same time. Unregulated is used to power the cassette motor.
Physical coding
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). Note the lower amplitude for the shorter periods.A circuit in the tape unit transforms the analog signal into a logical one or zero which is then transmitted to the computer via the tape connector. Inside the computer the first Complex Interface Adapter
MOS Technology CIA
The 6526/8520 Complex Interface Adapter was an integrated circuit made by MOS Technology. It served as a I/O port controller for the 6502 family of microprocessors, providing for parallel and serial I/O capabilities as well as timers and a Time-of-Day clock...
(6526) in the C64 senses when the signal goes from one to zero. This event is called trigger and causes an interrupt request
Interrupt request
The computing phrase "interrupt request" is used to refer to either the act of interrupting the bus lines used to signal an interrupt, or the interrupt input lines on a Programmable Interrupt Controller...
. 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.
Inside the tape device the read head
Tape head
A tape head is a type of transducer used in tape recorders to convert electrical signals to magnetic fluctuations and vice versa.-Principles of operation:...
signal is fed into an operational amplifier
Operational amplifier
An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output...
(1) whose output signal is DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
-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
Clipping (signal processing)
Clipping is a form of distortion that limits a signal once it exceeds a threshold. Clipping may occur when a signal is recorded by a sensor that has constraints on the range of data it can measure, it can occur when a signal is digitized, or it can occur any other time an analog or digital signal...
the sine formed signal. The positive and negative rails for all op-amps are wired to +5V DC and GND. The clipped signal therefore fits into the TTL electrical level window of the schmitt trigger step that in turn feeds the digital cassette port.
On the PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
version of the C64, the time granularity is 1.014 µs (for NTSC 0.978 µs). For a 300 bit/s data rate this means 3284 * 1.014 µs per data bit.
Once the bits can be decoded it's fed into a shift register
Shift register
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...
and compared to a special bit sequence continuously. This bit sequence can also be seen as a byte. A bit sequence match means the stream is byte synchronized. The first byte to compare with is called lead-in byte. If matched, it's compared to the sync byte as well.
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, $03, $02, $01.
Used with the PET, VIC-20, C64/128
There are at least four main models of the 1530/C2N Datassette:- The built-in Datassette in the original PET 2001: black cassette lid, five white keys, no tape counter, no SAVE LEDLEdLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
- 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 tape counter and a red SAVE LED
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 were compatible with all those computers, as well as the C128
Commodore 128
The Commodore 128 home/personal computer was the last 8-bit machine commercially released by Commodore Business Machines...
.
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 position. A small screwdriver
Screwdriver
A screwdriver is a tool for driving screws and often rotating other machine elements with the mating drive system. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver...
could 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 versus two s 'es) used on the original product packaging.
Used with the C16/116 and Plus/4
Similar in physical appearance to the 1530/C2N models is the Commodore 1531, made for the Commodore 16Commodore 16
The Commodore 16 was a home computer made by Commodore with a 6502-compatible 8501 CPU, released in 1984. It was intended to be an entry-level computer to replace the VIC-20 and it often sold for 99 USD...
and Plus/4
Commodore Plus/4
The Commodore Plus/4 was a home computer released by Commodore International in 1984. The "Plus/4" name refers to the four-application ROM resident office suite ; it was billed as "the productivity computer with software built-in"...
series computers. This had a Mini-DIN connector
Mini-DIN connector
The mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
in place of the PCB edge connector. This could 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
See also
- Fast loaderFast loaderA fast loader is a software program for a home computer - most commonly, the Commodore 64 - that accelerates the speed of file loading from the floppy disk drive.- Background :...
- IBM Cassette tapeIBM Cassette tapeOn early IBM personal computers, a cassette tape interface was provided to allow use of a cassette audio recorder to load and save data and programs. This option was only included on the original 5150 and 4860 ....
- Kansas City standardKansas City standardThe Kansas City Standard , or Byte standard, is a digital data format for audio cassette drives. Byte magazine sponsored a symposium in November 1975 in Kansas City, Missouri to develop a standard for storage of digital computer data on inexpensive consumer quality cassettes, at a time when...
- Magnetic tape data storageMagnetic tape data storageMagnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...
- MicroBeeMicroBeeMicroBee was a series of home computers by Applied Technology, later known as MicroBee Systems.The original MicroBee computer was designed in Australia by a team including Owen Hill and Matthew Starr...
External links
- Similar Commodore tape drives
- Datasette photos
- Description of tape format with conversion utilities and code
- C2N232 project to build a hardware adaptor/software program to archive Commodore Datasette files to a modern computer.
- DC2N Homepage Digital C2N replacement project.
- Sketchup model of the Commodore Datasette 1530. Sketchup model of the Commodore Datasette 1530.