8" Floppy Diskdrive

50 PIN EDGE or IDC at the computer

The 8-inch floppy drive interface originates from the Shugart SA800 and SA801 drives, introduced in 1977, and uses a 50-pin PCB edge-card connector (J1/P1). All odd-numbered pins carry ground, whilst even-numbered pins carry signals using active-LOW, open-collector TTL logic. The SA800 employs an AC induction spindle motor driven via a separate 6-pin AMP Mate-N-Lok power connector (P5/J5) supplying +24 V, +5 V, and −5 V; motor control is therefore not part of the 50-pin signal bus. This interface is a de facto industry standard that preceded the later 34-pin PC floppy bus and served as its direct ancestor.

Notes

• Direction is Computer relative Diskdrive
• All odd pins are GND, Ground
• All signals are active-LOW open-collector TTL; TRUE (asserted) = 0.0–0.4 V sinking up to 40 mA; FALSE (deasserted) = +2.5–+5.25 V open circuit
• Input lines (controller→drive) present 150-ohm impedance; the four multiplexed inputs (/DIR, /STEP, /WDAT, /WGAT) must be terminated with 150-ohm pull-up resistors at the last drive on a multi-drive cable
• /SEL1–/SEL4 (Drive Select) lines are inputs to the drive and activated by the controller; only one drive is selected at a time
• The SA801 variant adds a Sector output (pin 24) for hard-sectored disks; the SA800 leaves pin 24 unconnected
• /HLD (Head Load, pin 18) activates the read/write head solenoid; a minimum settle time is required after assertion before reading or writing
• Maximum recommended cable length is 10 feet, using AMP 1-583717-1 twisted-pair or 3M Scotchflex 3415-0001 flat ribbon cable
• The TG43 (Track Greater Than 43) signal, required on many 8-inch drives to reduce write current beyond track 43, is absent from this connector definition and must be managed separately when adapting 8-inch drives to later controllers

Signals

• /REDWC — Reduced Write Current; asserted by the controller for inner tracks (beyond track 43) on drives that do not support TG43 internally
• /FD2S — Disk Is Two-Sided; drive output indicating a double-sided diskette is loaded
• /DCG — Disk Changed / Door Open; drive output indicating the diskette has been ejected or the door opened since the last drive select
• /SIDE — Side Select; controller output selecting which recording surface (head 0 or head 1) is active on double-sided drives
• /DLOCK — Door Lock; controller output engaging the drive door latch to prevent diskette removal during operation
• /HLD — Head Load; controller output commanding the drive to lower the read/write head onto the diskette surface
• /INDEX — Index Pulse; drive output producing one pulse per disk revolution marking the start of track sector 0
• /READY — Ready; drive output asserted when the drive is selected, the diskette is loaded, and the spindle is at speed
• /SEL1–/SEL4 — Drive Select 1–4; controller outputs selecting one of up to four drives on a shared cable; only one should be asserted at a time
• /DIR — Direction Select; controller output setting the direction of head stepping (low = step inward toward centre)
• /STEP — Step; controller output; each active-LOW pulse moves the head one track in the direction set by /DIR
• /WDAT — Write Data; controller output carrying the flux-transition data stream during write operations
• /WGAT — Write Gate; controller output enabling the write circuitry; must be asserted before write data is valid
• /TR00 — Track 00; drive output asserted when the read/write head is positioned at the outermost track (track 0)
• /WPROT — Write Protect; drive output asserted when the loaded diskette has its write-protect notch covered
• /RDATA — Read Data; drive output carrying the raw flux-transition data stream read from the diskette surface

References

• Shugart SA800-801 Diskette Drive OEM Manual (1977)

Category:Data Storage Connectors