Commodore 1551

Commodore 1551

Type:	Disk
Producer:	Commodore
Price:	About $400
Released:	1984
Discontinued:	1986
Processor:	6502 clone
Memory:	< 1MB
OS:	—
Info:	Commodore 1551 floppy disk unit

The Commodore 1551 or 1551 is a floppy disk drive for the budget 264-series of home computers. Unlike its notoriously sluggish forerunner, the 1541 floppy disk C64 unit, the 1551 uses an included cartridge instead of the serial port. The cartridge is recognized by the Plus/4 Kernal. This made data transfer four times faster (and even faster when used with disk accelerators).

Its attractive styling matches the dark design of the Plus/4. It uses regular 5 1/4-inch disks but was not compatible with the older 1541 model.

Commodore 1551 drive showing also the connector

Owners could cobble together two 1551s for a dual-floppy solution, though it needed a bit of tricky hardware hacking.

LED Error Flash Codes[edit | edit source]

After the 1551 gets switched on it may happen that the drive LED starts flashing right away in a certain pattern, depending on what error it wants to show.

The pattern looks like so, it flashes a certain amount of times (see table below), then there is a short pause, then it flashes again the same amount of times,

the flashing goes on until the drive gets switched off or the computer sends a hard reset (e.g. switching it off and on).

Number of Flashes	Issue
1	RAM, zero page $02-$ff
2	ROM checksum
3	RAM $0100 - $07ff
4	communication (after first acces from C16/+4) failure in cable or paddle

The last one only happens after the computer sends a command what does not get recognized by the drive.

If the LED is contiguously flashing then it indicates a normal operating error where you're able to check with a PRINT DS$ on a Plus4 or C16 and continue with the next command.