SCSI2SD old: Difference between revisions

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== Specifications ==
== Specifications ==
* Fast Narrow Single-Ended SCSI-2
* Fast (10MHz) Narrow (8-bit parallel) Single-Ended SCSI-2


== Why ? ==
== Why ? ==
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* SCSI Terminator.  [http://au.element14.com/texas-instruments/uc5601dwpg4/scsi-terminator-18-line-5v-soic28/dp/1234991 TI UC5601DWPG4]
* SCSI Terminator.  [http://au.element14.com/texas-instruments/uc5601dwpg4/scsi-terminator-18-line-5v-soic28/dp/1234991 TI UC5601DWPG4]
* AT90USB1286
* AT90USB1286
** USB Host functionality
** Sources/Sinks 40 mA per I/O pin (Specs require 48mA, but this includes a very large safety margin).
** TTL (5V) I/O output
** Up to 48 [http://en.wikipedia.org/wiki/Three-state_logic tri-state] GPIO pins (need minimum of 18 for SCSI data + control signals)
* 50 pin IDC header
* 50 pin IDC header
* USB socket
* USB socket
* 5V supply via Molex drive connector
* 5V supply via Molex drive connector
* (Check) 3.3v to 5v level converter ?
* [http://au.element14.com/texas-instruments/cd74ac280e/logic-parity-gen-chker-9bit-14dip/dp/1753467 TI CD74AC280E] Parity checker/generator.
* [http://au.element14.com/texas-instruments/cd74ac280e/logic-parity-gen-chker-9bit-14dip/dp/1753467 TI CD74AC280E]/74HC280 Parity checker/generator.


== SCSI Electrical Interface ==
== SCSI Electrical Interface ==
SE and LVD devices may co-exist on a SCSI chain, but the chain will be reduced to SE functionality.
SE and LVD devices may co-exist on a SCSI chain, but the chain will be reduced to SE functionality.
[http://en.wikipedia.org/wiki/Open_collector Open collector] signals are used. There are 8 (narrow SCSI) or 16 (wide SCSI) data signals, 1 parity signal, and 9 control signals.


=== Single Ended (SE) ===
=== Single Ended (SE) ===
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* TTL logic levels.
* TTL logic levels.
* Up to 40MB/sec (Ultra Wide SCSI).
* Up to 40MB/sec (Ultra Wide SCSI).
* Terminated by 220ohms to TERMPWR, 330ohms to ground.
* Output signals:
** Signal asserted (true): 0V to 0.5V, up to 48mA sinking current.
** False: 2.5V to 5.25V
* Input signals:
** Signal asserted (true): 0V to 0.8V
** False: 2V to 5.25V


=== Low-voltage differential (LVD) ===
=== Low-voltage differential (LVD) ===
* [http://en.wikipedia.org/wiki/RS-485 RS-485] compatible.  Either LVD SCSI Transceivers or RS-485 transceivers may be used.
* [http://en.wikipedia.org/wiki/RS-485 RS-485] compatible.  Either LVD SCSI transceivers or RS-485 transceivers may be used.
* Up to 320MB/sec (Ultra-320 SCSI).
* Up to 320MB/sec (Ultra-320 SCSI).
== SCSI2USB Design ==
=== Internal Termination ===
* Should be switchable, on and off.
* Use a purpose-built IC.
=== Parity Checker ===


== Links ==
== Links ==
The following projects will be of great help:
=== Projects ===
* [http://micha.freeshell.org/ramdisk/index.php AVR based SCSI RAM disk ] (Open-source AVR microcontroller SCSI interface)
* [http://micha.freeshell.org/ramdisk/index.php AVR based SCSI RAM disk ] (Open-source AVR microcontroller SCSI interface)
* [http://www.fourwalledcubicle.com/LUFA.php LUFA] Open-source AVR microcontroller USB stack.
* [http://www.fourwalledcubicle.com/LUFA.php LUFA] Open-source AVR microcontroller USB stack.
* [http://atari.nvg.org/parity/parity_gen.html SCSI parity generator]
* [http://atari.nvg.org/parity/parity_gen.html SCSI parity generator]


Reference information:
=== References ===
* [http://focus.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=SLLA035&track=no Interface Circuits for SCSI Design Notes]
* [http://focus.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=SLLA035&track=no Interface Circuits for SCSI Design Notes]
* [http://dsaprojects.110mb.com/electronics/data_book/ic_technology.html] IC logic families and typical propagation delays.

Revision as of 11:15, 28 September 2011

A device that presents a USB Mass Storage device as a Direct Access device to a SCSI controller.

Specifications

  • Fast (10MHz) Narrow (8-bit parallel) Single-Ended SCSI-2

Why ?

Because there are many vintage computers out there that require a 50-pin SCSI drive to boot from. Such disks are only available second-hand, and it's getting harder and harder to find a working disk.

Alternatives

  • The price of commercial SCSI converters can be much higher than the vintage computers they are used in. However, these devices are still readily available.
  • 50pin to 68pin or 80pin SCSI converters allow the use of newer drives. Availability of new SCSI SCA (80 pin) drives is limited to prohibitively expensive 15K RPM "enterprise" drives.

Why USB ?

Because USB Mass Storage devices already understand SCSI commands.

Parts Required

  • SCSI Terminator. TI UC5601DWPG4
  • AT90USB1286
    • USB Host functionality
    • Sources/Sinks 40 mA per I/O pin (Specs require 48mA, but this includes a very large safety margin).
    • TTL (5V) I/O output
    • Up to 48 tri-state GPIO pins (need minimum of 18 for SCSI data + control signals)
  • 50 pin IDC header
  • USB socket
  • 5V supply via Molex drive connector
  • TI CD74AC280E Parity checker/generator.

SCSI Electrical Interface

SE and LVD devices may co-exist on a SCSI chain, but the chain will be reduced to SE functionality.

Open collector signals are used. There are 8 (narrow SCSI) or 16 (wide SCSI) data signals, 1 parity signal, and 9 control signals.

Single Ended (SE)

  • Still supported on new U320 drives.
  • TTL logic levels.
  • Up to 40MB/sec (Ultra Wide SCSI).
  • Terminated by 220ohms to TERMPWR, 330ohms to ground.
  • Output signals:
    • Signal asserted (true): 0V to 0.5V, up to 48mA sinking current.
    • False: 2.5V to 5.25V
  • Input signals:
    • Signal asserted (true): 0V to 0.8V
    • False: 2V to 5.25V

Low-voltage differential (LVD)

  • RS-485 compatible. Either LVD SCSI transceivers or RS-485 transceivers may be used.
  • Up to 320MB/sec (Ultra-320 SCSI).

SCSI2USB Design

Internal Termination

  • Should be switchable, on and off.
  • Use a purpose-built IC.

Parity Checker

Links

Projects

References

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