ACC Microelectronics KT-204

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ACC Microelectronics KT-204
ACC Microelectronics KT-204.jpg
Bus type ISA
Bus width 8-bit
Bus speed 8 MHz
Manufacturer ACC Microelectronics
Chipset MCS3201FN
Compatible with PC Floppy
Connectors None
Requires -5VDC? No
Requires -12VDC? Yes
Config method Jumpers
Floppy Controller
Floppy buses 2
Drives per bus 2
Secondary? Yes
ROM type 28-pin JEDEC
Driver N/A

The KT-204 is an 8-bit floppy controller capable of supporting up to four 1.44MB drives. It includes a boot ROM, allowing the system to boot from a floppy disk even when the BIOS does not support doing so (e.g. booting from 1.44MB disks on an XT.)


Drive/size SW1
Drive 0 1 2
Drive 1 3 4
Drive 2 5 6
Drive 3 7 8
360 K on on
720 K on off
1.2 M off on
1.44 M off off
J1 Purpose
open Primary FDC controller (base I/O at 0x3F0)
closed Secondary FDC controller (base I/O at 0x370)

The boot ROM is always at segment CA00 regardless of the jumper setting.

Internal connectors

First floppy bus (drives 0 and 1)
Second floppy bus (drives 2 and 3)

Additional photos


During POST, a banner similar to the following is displayed:

ACC Microelectronics
Advanced FDC Firmware v1.0c

The ROM appears at CA00:0000 to CA00:07FF regardless of the J1 setting.

The card's BIOS only appears to support the controller at the primary address (0x3F0). When set to the secondary address (0x370) the POST freezes unless there is another primary floppy controller present. Booting off the secondary controller does not seem to be possible. This was tested with BIOS v1.0c on a card with no physical jumper installed at J1, so it is possible this BIOS had secondary support removed.


The card seems to run floppy drives slightly slower than others (possibly due to the custom BIOS.) It also struggles reading some marginal floppies that other newer cards appear to be able to read without problem, using the same physical drive.

Related links

  • ROMs - acc-105b.rom (ACC Microelectronics FDC ROM v105B) is a ROM for this card. The signature at the end of the file states v1.0b so it is unclear where the "5" comes from.