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Connecting an FDD for PC/AT compatible computer to PC-9821
( Implementation )


Introduction

As a result of testing multiple FDDs, we were able to operate it on the PC-9821 Ls12 by modifying it as shown in the drawing shown in the table below.

In the table below, plot diagrams and reference photographs that outline the remodeling points are organized by FDD. After checking the outline of the modification contents in the drawing, please observe the difference before and after the modification with the reference photo. Even if the drawings are drawn too finely, it will only be difficult to deal with differences in production lots, so I dare to list only the important items.


Application to other models

The materials shown in the table below are all based on the assumption that the PC-9800 series is used, but they can be applied to other models.

For example, in the case of the MSX series model with a 34-pin interface, the modification to enable output of the READY signal is performed as shown in the figure. Replacing the Density (Mode Select) signal can be omitted. Instead, it seems that it is necessary to fix the FDD operation mode to 2DD mode and additionally modify the Drive Select and Motor ON signals.

For more information, please see the article "FS-FD1A drive conversion" by Niga HP on PS2Linux DASH. (The author of this article does not own an MSX and has not been able to verify this.)


Common precautions

The precautions common to all the drawings shown in the table below are shown below.

  • In an FDD with a 34-pin interface, with some exceptions, the 360/300 signal input to pin 2 of the FDD must be inverted using a 74HC14 or the like.
  • In general 3.5-inch FDD, there are FDD that does not require inversion of 360/300 signal and FDD that requires it, so in consideration of the uniformity of the appearance of the drawing, the matters related to 74HC14 are described in the special notes. On the other hand, the thin FDD basically needs to invert the 360/300 signal, so 74HC14 is shown in the drawing.
  • When connecting a PC-9821Xa7 or later desktop machine and FDD with a flat cable, modifications related to so-called "reversible cables" and "reversible connectors" must also be made. Specifically, it is necessary to replace the flat cable with one whose terminals are crimped in the same direction, or to insert a conversion board between the existing flat cable and the modified FDD to absorb the difference in terminal direction.
  • There are two types of Ready signals: one is to use a regular Ready signal and the other is to substitute a pseudo Ready signal. In the case of using a pseudo-Ready signal, there is a possibility of causing some problems if the wiring is simply connected. Please refer to "Consideration and Verification of MSX FDD READY Signal" by HP on PS2Linux DASH for the countermeasure.
  • In the drawing, the Disk Change signal is shown to be output to pin 33. However, as described in the overview section, this is not actually used, so the modification is omitted in the FDD shown in the reference photo.

List of FDD modified drawings

The following is a list of FDD modification drawings and reference photos, as well as the results of operation tests after modification. When referring to the drawings and reference photos, be sure to also refer to the special notes at the end of the list.

List of FDD modification results
FDD
Model No.
*1
Drawings Reference
photo
Available
format types
for PC-9821
Note
Before
renovation
After
renovation
2HD
(1.44)
*2
2HD
(1.23)
*3
2DD
FD1231T
(FDN303)
[6pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK OK *4
*5
*6
FD1231M
(FDN303)
[6pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK OK
MPF920
(BH9558KV)
[35pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*8
MPF920-E
(CXA8061Q)
[42pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *15 *7
*9
D353M3D
(NCL039)
[35pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *16 *7
*10
D353-T5
(NCL032)
[32pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
YD-702D
-6537D-A
(BU6108K)
[14pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
YD-702D
-6638D
(BH9522KS2)
[19pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
YD-702D
-6639D
(BH9522KS2)
[19pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK

For this FDD, it is necessary to modify the jumper. For details of jumpers, refer to the separate drawing ( Jumper Setting Table ( Y-E DATA YD-702D-6639D ) ) .
Reference photo ( Before renovation,After renovation )

JU-256A
216P
(FQL02030B4)
DXF PDF whole Partial
details
whole Partial
details
OK OK *7

In order to modify this FDD, it is necessary to remove and reattach the FPC and FFC cables for the stepping motor of the head in addition to the control board at the same time.

Once the control board is removed, it is necessary to adjust the position of various sensors in micrometer steps. Therefore, although reference drawings of this FDD are provided, we recommend avoiding modifications as much as possible.

In the case of switching only between Disk Change and Ready signals, there is a method of modification without removing the control board. Specifically, after moving the head to the innermost side, "R45" and "R46" related to switching are modified through the gap between the head and frame inside the FDD. With this method, misalignment of various sensors can be prevented.

JU-256A
637PC
(DN8655FA)
[28pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*11
JU-257A
137P
(BH9571KV)
[24pin]
DXF PDF whole Partial
details
whole Partial
details
OK *7
*17
FD-235HG
-A304-U5
(TB6048)
[31pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*12
FD-235HG
-C235-U
(BH9521KS2)
[26pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*13
FD-235HG
-6360-U
(BH9503GKS2)
[10pin]
DXF PDF whole Partial
details
whole Partial
details
OK *7

For this FDD, it is necessary to modify the jumper. For details of jumpers, refer to the separate drawing ( Jumper Setting Table ( TEAC 3-row type ) ) .
Reference photo ( Before renovation,After renovation )

FD-235HG
-7304-U5
(TB6022AF)
[10pin]
DXF PDF whole Partial
details
whole Partial
details
OK *7
FD-235HF
-7304-U5
(BH9506GKS2)
[10pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*19
Z1D
(BH9547KV)
[4pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
Z1DA-89A
(61828)
[4pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
MF-355F
-3490UC
(U262P128)
[48pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
OSD-FIL
(61838A)
[4pin]
DXF PDF whole Partial
details
whole Partial
details
OK *7
TFD-310
(DN8862FAQ)
[19pin]
DXF PDF whole Partial
details
whole Partial
details
OK *7
MPF820
(BH9556KV)
[15pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
D353F3
(NCL053)
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
YD-702J
-6037J
(BH9522KS2)
[19pin]
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*18
FD-05HG
-5708-U
(NN8863FAW)
[18pin]
DXF PDF whole Partial
details
whole Partial
details
OK ? *7
*14
FD3238T
(FDN305)
[6pin]
DXF PDF whole Partial
details
whole Partial
details
OK ? *7
MF355H
-325MS
(U262P149)
DXF PDF whole Partial
details
whole Partial
details
OK OK *7
*20
  • *1
    The string in round brackets indicates the model number of the control IC, and the string in square brackets indicates the number of the pin outputting the Ready or pseudo Ready signal of the control IC.
  • *2
    The format type of the disk is 2HD.
  • *3
    The format type of the disk is 2HD.
  • *4
    If the access lamp does not light, shorting the HDR jumper will light the FDD access lamp.
  • *5
    The information "pin 26 and pin 42 of FDN30x are connected" in the drawing was provided by Crusher-K.
  • *6
    FD1231H can also be used with similar modifications.
  • *7
    When inputting a 360/300 signal to the Density pin, the signal should be inverted using 74HC14 or similar. (The inverting circuit may not be shown in the reference photo. )
  • *8
    It seems that YD-702D-6238D can be used with similar modifications.
  • *9
    It seems that MPF920-F and MPF920-L can be used with similar modifications.
  • *10
    The D359M3D may also be usable with similar modifications. However, since the pattern of the control board is different, it is necessary to carefully examine the signal extraction location based on the reference photo.
  • *11
    JU-257A607PC can also be used with similar modifications. However, additional work to short the "R71" is required. Also, it seems that JU-256A347P can be used with similar modifications.
  • *12
    It seems that FD-235HG-B380-U can be used with similar modifications.
  • *13
    It seems that FD-235HG-C122-U5 and FD-235HG-C635-U can be used with similar modifications.
  • *14
    It seems that FD-05HG-8745-U can be used with similar modifications.
  • *15
    2DD can also be read/write, though unstable (not sure if it can be formatted) .
  • *16
    2DD is also readable and writable (not sure if it can be formatted) .
  • *17
    The JU-256A048PC may also be usable with similar modifications. However, since the pattern of the control board is different, it is necessary to carefully examine the signal extraction location based on the reference photo.
  • *18
    The specific cause is unknown, but we have confirmed that there are some units that do not work properly even after modification for some reason.
  • *19
    It seems that FD-235HF-7291-U5 can also be used with similar modifications.
  • *20
    It seems that MF355H-348MN can be used with similar modifications. However, the modification to invert and input the 360/300 signal by cutting pin 13 while the control board is fixed to the FDD housing requires removal and reinstallation of the 26-pin terminal installed on the control board, making the modification highly difficult. Therefore, it is better to prepare a conversion board separately from the FDD.

The FD3238T listed in the above list is equipped with the same FDN30x series as the FD1231T as a control IC. I expected that 2DD could be used if the same modification as FD1231M was performed, but in reality 2DD could not be used.

If you modify the FD3238T in the same way as the FD1231M and then connect the FD3238T to the PC-9821 Ls12 to access the FD, the disk will be recognized but will be displayed as "unformatted" and will stop. After that, any attempt to format it will fail.

Upon closer examination, it was found that even if it was modified, the limit was to invert the 360/300 signal and input it, and it was concluded that 2DD could not be used.

The cause is unknown, but it is believed to be an abnormality in the control of the head section. If the cause can be identified, it will be possible to use 2DD on the PC-9821 series.


Reference

Although the DF354N178F can output the Ready signal, for some reason it did not work well with the PC-9821 Ls12. The Ready signal output point is shown for reference.

DF354N178F Reference
Whole board
Ready signal output point


References
Ematei na recycle
HAMLIN's PAGE
Dorcom [14183] Using FD1231H with PC-98


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