CD-ROM Mitsumi

Proprietary Mitsumi 40-pin IDC interface used by LU002S, LU005S, FX001 and FX001D drives on ISA soundcards in the early 1990s.

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CD-ROM Mitsumi – 40-pin IDC header 40 pin IDC male connector at the controller and CD-ROM.

CD-ROM Mitsumi – 40-pin IDC header 40 pin IDC female connector at the cable.

The Mitsumi proprietary CD-ROM interface is a 40-pin IDC parallel bus developed in the early 1990s for the company’s first-generation drives (LU002S, LU005S, FX001, and FX001D). It is electrically incompatible with both SCSI and the later ATAPI/ATA standard, operating instead as an 8-bit parallel bus tied to the ISA expansion slot at I/O base addresses typically 0x300 or 0x340. The interface carries two address lines (A0/A1), an 8-bit data bus (DB0–DB7), read/write strobes, a bus-enable line, and optional DMA request/acknowledge and interrupt signals. Controllers were integrated into ISA soundcards of the era, including the Creative Sound Blaster CT1750 variant; the Linux kernel driver mcdx documents the register-level protocol for this interface.

PinNameDescription
1A0Address Bit 0
2GNDGround
3A1Address Bit 1
4GNDGround
5n/cNot connected
6GNDGround
7n/cNot connected
8GNDGround
9n/cNot connected
10GNDGround
11n/cNot connected
12GNDGround
13INTInterrupt
14GNDGround
15REQData request For DMA
16GNDGround
17ACKData Acknowledge For DMA
18GNDGround
19RERead Enable
20GNDGround
21WEWrite Enable
22GNDGround
23ENBus Enable
24GNDGround
25DB0Data Bit 0
26GNDGround
27DB1Data Bit 1
28GNDGround
29DB2Data Bit 2
30GNDGround
31DB3Data Bit 3
32GNDGround
33DB4Data Bit 4
34GNDGround
35DB5Data Bit 5
36GNDGround
37DB6Data Bit 6
38GNDGround
39DB7Data Bit 7
40GNDGround

Notes

  • All even-numbered pins (2–40) are ground; odd pins carry signals or are left unconnected.
  • Pins 5, 7, 9, and 11 are not connected and must be left open.
  • Although the 40-pin IDC ribbon physically resembles a standard ATA cable, the electrical signalling is entirely incompatible with ATA/ATAPI; substituting an IDE cable for mechanical convenience does not make the drives interchangeable.
  • DMA and IRQ support is driver-dependent. The MTMCDE.SYS DOS driver supports DMA/IRQ operation; MTMCDS.SYS uses software polling only. Many ISA soundcard implementations (including the Creative CT1750 Mitsumi port) bypassed DMA/IRQ entirely, leaving REQ, ACK, and INT functionally unused.
  • The newer Mitsumi FX-series drives that adopted ATAPI must NOT be connected to this proprietary port; OEM controller documentation explicitly warns against mixing the two generations.
  • Analog audio from the drive is carried on a separate 4-pin connector, not the 40-pin ribbon. The Mitsumi audio pin order (signal–GND–signal–GND) differs from other vendors; reversing the cable can short the audio output.

Signals

  • A0, A1 — Two-bit register address bus; selects which internal drive register is accessed during a read or write cycle.
  • INT — Interrupt output from the drive to the host; signals command completion or an error condition. Optional — may be left disconnected when the driver uses software polling.
  • REQ — DMA request output; asserted by the drive when it is ready to transfer a byte via DMA. Optional — unused in polled-mode driver configurations.
  • ACK — DMA acknowledge input; asserted by the ISA DMA controller to confirm a DMA transfer cycle. Optional — unused in polled-mode driver configurations.
  • RE — Read Enable (active-low strobe); asserted by the host to latch data from the drive onto DB0–DB7.
  • WE — Write Enable (active-low strobe); asserted by the host to write a command byte from DB0–DB7 into the addressed drive register.
  • EN — Bus Enable; enables the drive’s data bus drivers, allowing DB0–DB7 to be driven during a transfer.
  • DB0–DB7 — 8-bit bidirectional parallel data bus carrying command bytes to the drive and status/data bytes from the drive.

References

Category:Data Storage Connectors