VC1571

VC 1571

The floppy disk drives VC 1570 and VC 1571 are 5¼ inch drives for the home computer Commodore C128 , but they can also be used on the C64 . Internally they work with Commodore DOS version 3.0 or (in the C128DCR) version 3.1.

Characteristics

In terms of the shape of the case, the 1571 adapts to the design of the C128 (it looks like a larger 1541 II); the 1570, on the other hand, has the same beige case as the 1541C. The drives run noticeably quieter than older models and also produce less heat, so that - in contrast to some 1541s - no thermal problems (misalignment etc.) occur despite the integrated power supply unit.

The drives have 2 modes: 1541 (emulation) and 1571 or 1570 (native) mode. By default, the former is active when switching on and the internal 6502 CPU clocks with 1 MHz, the drive switches to native mode with 2 MHz clock as soon as a C128 accesses it.

On the C128, the 157x implements a much faster data transfer to the computer than the VC1541 (approx. 7 times faster), for which a line of the serial bus that has not been used until then is used for hardware handshaking (so-called fast serial transfer). A C64 can be upgraded on the hardware side for this data transfer. This hardware configuration also enables a special transmission mode (“burst mode”) that is up to 30 times faster than the standard transmission between the C64 and 1541 and requires special programming on the computer side.

On the C64, VC20 etc. In the 1541 mode, the drives behave like a 1541 (although the second disk side and MFM formats can also be accessed here with appropriate programming, but only at 1541 speed). Since almost the same DOS is used in the 1541 mode as in the 1541, the majority of the C64 fast chargers (including those of the Action Replay 6 and Final Cartridge 3) also work with the 157x, only very hardware or timing-specific tricks fail.

Like the VC1541, the VC157x normally uses GCR recording. In addition, it has an additional controller (WD 1770) for the MFM recording method and can therefore also read the CP / M and MS-DOS floppy disks usually recorded in this method . It is thus possible to copy files from a conventional PC to the C128 and vice versa (e.g. with the programs "Big Blue Reader" and "Little Red Reader"). However, this is only possible for PC and PC / XT floppy disks with a maximum capacity of 360 kB ; the VC157x cannot read the HD disks of the PC / AT and later models with 1.2 MB.

Data capacity

While the 1570, like the 1541, has only one read / write head and can therefore write to floppy disks like this only by turning them over twice on one side, the 1571 has two heads so that floppy disks can be used on both sides. Because of the reverse direction of rotation and the four-track offset of the head on the back of the disk, the two methods "flip" and "second head" are not compatible with each other; Double-sided reversible diskettes created on the VC1541 must also be reversed in the VC1571.

The maximum mechanical capacity is 400 kB, whereby the native Commodore format formats the floppy disk with 340 kB (2 × 35 tracks, 1360 blocks of 256 bytes each). (For comparison: IBM DD 5.25 "disk initially 320 kB, from MS-DOS 2.0 360 kB.)

Under normal circumstances, 254 bytes of 1328 blocks can be used for data, i.e. 337,312 bytes per diskette or just under 330 Kbytes; the rest is used for the file system .

In addition, the format of the VC1541 (35 tracks of 683 blocks each = 170 kB, of which almost 165 kB are normally usable) can be read, written and formatted.

variants

The 157x is available as an independent drive in beige (with integrated power supply), the 1571 is also built into the C128D and C128DCR.

Internal drive in the C128D

The drive in the (plastic) C128D corresponds to an external 1571 without a housing. The controller board, which is independent of the main board of the C128, has been changed in layout and size compared to the board of the external 1571, but the circuit and components are identical. The first version of CBM DOS 3.0 had problems reading sectors on the second side of the diskette from diskettes in 1571 format (repositioning of the read / write head after writing a sector on the second side of the disk). This bug was fixed in later versions of the CBM DOS. The drive, like the external 1571, cannot read copy-protected floppy disks in 1541 format in certain cases. Likewise, some fast chargers designed for the 1541 will not work.

Internal drive in the C128DCR

As part of the redesign of the main board of the C128DCR (CR = cost reduction , with the aim of reducing the number of components required), the controller board of the internal 1571 drive, which is still independent in the C128D, was integrated into the redesigned main board of the C128DCR. The main feature of the integrated controller is the use of two new components that control the drive itself and combine various components of the previous circuit. A new version of the CBM DOS 3.1 was delivered with this drive, which, in addition to eliminating errors compared to older versions, also includes an adaptation to the two new controller modules. Not only this new CBM-DOS version, but also the new modules led in some cases to an extended incompatibility with the 1541 drive, especially for C64 games with floppy disk fast loaders or copy protection.

1570

The 1570 consists of the circuit board of the 1571, a drive from the manufacturer Alps with only one read / write head, white painted front panel made of brown plastic and a light barrier for index hole recognition (largely identical to the drives from Alps in the 1540/41), an additional circuit board with a power supply assembly (electrically similar to the power supply assembly of the 1540/41) and the housing of the 1541C in white color. The firmware (CBM DOS 3.0) was derived from the firmware of the 1571 and essentially contains the adjustments for the drive with only one read / write head.

In contrast to 1571, at least in Germany, the 1570 was already available at the beginning of sales of the C128. Commodore developed the 1570 probably only because the 1571 was significantly behind schedule and the boards and housings for the 1571 should not be produced endlessly in stock; Furthermore, the 1541 series was no longer up-to-date for the C128, as this, as a professional computer, should have a drive from the start of sales that was faster and (important for CP / M) MFM-capable.

Variants not implemented

1572

At CES 1985 the 1572 was presented, which was a floppy disk station with two 1571 drives, which visually resembled a double-wide 1571 with two slots and toggles. It is questionable whether there are any functional prototypes of this drive.

1571 II

There were plans to bring out a "1571 II" with a separate power supply (similar to the 1541 II), which should have worked with the slightly corrected DOS 3.1 of the C128DCR, which is less compatible with DOS 3.0 and the versions for the 1541 series. Because of Commodore's fixation on the Amiga computers, this drive no longer appeared.

JiffyDOS for the 157x

For the 157x series, as for other CBM drives, there is also a fault-corrected JiffyDOS in addition to other third-party DOS ROMs , which among other things no longer occurs with the C128D and increases the compatibility of the drive in the C128DCR.

Overview specifications VC 1570/1571

Disc type: 5¼ inches
Recording format: GCR , MFM , single-sided (1571 also double-sided), double density
Formatting: 35 (1570) or 2 × 35 (1571) tracks, 17-21 sectors per track, 256 bytes per sector (of which 254 bytes can normally be used for data)
CPU: MOS Technology 6502 A with 1–2 MHz
RAM: 2 KB
ROM: 32 KB
Transfer protocols: standard (like 1541) as well as fast serial and burst mode (like 1581, with C128)
Interface: CBMs "serial IEEE-488" ( CBM bus , via DIN connector)

literature

Karsten Schramm: The 1570/1571 floppy. The manual for programming the 1570 and 1571 floppy. With a detailed listing of the DOS operating system routines . Markt-und-Technik-Verlag, Haar near Munich 1986, ISBN 3-89090-185-9 , download .