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WD-27X.DOC Documentation of ST-238R Drive and WD-27X Controller
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Seagate 5.25" Half-Height Disk Drives


Seagate Drive ST-225 ST-238R ST-251R ST-251 ST-277R

Bytes Unformatted 25.6 Mb 38.4 Mb 51.2 Mb 51.2 Mb 76.9 Mb
Bytes Formatted MFM 21.4 Mb - - 42.8 Mb -
Bytes Formatted RLL - 32.7 Mb 43.6 Mb - 65.5 Mb

Cylinders 615 615 820 820 820
Heads 4 4 4 6 6
Platters 2 2 2 3 3
W.P.C. 300 616 821 off 821
R.W.C. 615 615 820 820 820
IBM Drive Type 2 (6) (?) 44 (?)

Seek Time 60 ms 55 ms 50 ms 45 ms 40 ms

Bytes per Cylinder 34816 53248 53248 52224 79872
Tracks 2460 2460 3280 4920 4920
Bytes per Track 8704 13312 13312 8704 13312
Sectors per Track 17 26 26 17 26
Bytes per Sector 512 512 512 512 512


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Seagate ST-238R Jumper Settings


Looking at the bottom (circuit card side) with the edge connectors
UP there are eight pairs of jumpers visible, 16 pins total. From
left to right those jumper pairs are:

* 1 * Drive Select 1 (straight cable from HDC )
2 Drive Select 2 (5 wires twisted in cable)
3 Drive Select 3 open
4 Drive Select 4 open
5 Life Test open
6 Write Fault open
7 Recovery Mode open
8 Radial Mode open

3.1 Drive Select

DRIVE SELECT enables the controller to select and address the drive.
Control cable interface options use either Daisy-Chain or Radial
configuration.

3.1.1 Daisy-Chain

Drives must be selected as either DRIVE SELECT 1,2,3 or 4, so that only
one DRIVE SELECT line activates a device. To select, install the
shorting bar at the appropriate position. The last drive in the chain
must have a 220/330 ohm resistor termination pack on the PCB.

3.1.2 Radial Option

By shorting pins 1 and 2 the radial option is enabled. Drives
configured to this option are always selected and respond to all control
signals issued on the attached control cable. The resistor termination
pack remains installed on each radially-configured drive.

3.2 Write Fault Reset Option

The WRITE FAULT signal may be internally latched. This latch may be
cleared when DRIVE SELECT goes false (if pins 5 and 6 [write fault] are
shorted). The standard configuration, with the shorting block removed,
will cause WRITE FAULT to go false when WRITE GATE goes false.

3.3 Life Test

This function is used during the manufacturing process and is not
recommended for field use. When pins 7 and 8 are shorted, the stepper
motor will continuously seek between track 0 and the maximum cylinder
and will ignore control signals sent via the interface.

3.4 Recover Mode Option

The ST-238R may be configured for the RECOVERY MODE feature by shorting
pins 3 and 4. This option enables the read/write heads to micro-step.
This repositioning option may be used after the controller has completed
its retry options on a read error. Refer to section 4.6 for a detailed
discussion. [ 4.6 reveals that this option allows reads between tracks
in up to eight micro-steps IF the controller supports this feature. This
is intended to be used for recovering unreadable data ].


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Western Digital WD1002-27X Controller


There are six versions of the WD1002-27X Controller:

ROM BIOS I.D. Feature Description

(1) --- none ---- F000 no ROM BIOS or mounting bracket
(2) --- none ---- F007 no ROM BIOS w/ mounting bracket
(3) 62-000087-030 F019 ROM BIOS 0 (standard)
(4) 62-000088-030 F022 ROM BIOS 1 (26 to 17 sector)
(5) 62-000089-030 F016 ROM BIOS 2 (26 sector)
(6) 62-000094-032 F301 Auto-Configuration ROM BIOS


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WD-27X Disk Parameter Table (BIOS 62-000089-030)


C800:0041 D5 03 05 D6 03 D6 03-0B 07 FF 03 00 00 00 00 00
C800:0051 DB 03 07 DC 03 DC 03-0B 00 FF 03 00 00 00 00 00
C800:0061 64 02 04 65 02 65 02-0B 07 A7 03 00 00 00 00 00
C800:0071 67 02 04 68 02 68 02-0B 07 AC 03 00 00 00 00 00


RLL Table begins at C800:0041 and contains four Drive Types.


Type Cyl Heads ReadWrC PreComp ECC CCB Std Format

0 981 5 982 982 11 7 255 3 x
1 987 7 988 988 11 0 255 3 x
2 612 4 613 613 11 7 167 3 x
* 3 * 615 4 616 616 11 7 172 3 x


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WD1002-27X Step Rate Tables


The CCB Option Byte and onboard MicroProcessor determine Step Rate.


MPU 1015-14 CCB Step Rate
0 3000 usec
1 3000 usec
2 3000 usec
3 3000 usec
4 200 usec
5 70 usec
6 3000 usec
7 3000 usec

MPU 1015-24 CCB Step Rate
and MPU 1015A-24 0 3000 usec
1 45 usec
2 60 usec
3 18 usec
4 210 usec
5 75 usec
6 30 usec
7 18 usec

MPU 1015-25 CCB Step Rate
0 3100 usec
1 46.5 usec
2 22.5 usec
3 10.5 usec
4 202.5 usec
5 70.5 usec
6 38.5 usec
7 10.5 usec

MPU 1015E-08 CCB Step Rate
0 3300 usec
1 24 usec
2 24 usec
3 11 usec
4 24 usec
5 24 usec
6 24 usec
* 7 * 11 usec


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WD-27X Jumper Settings (BIOS 62-000089-030)


Drive Type: Device 0 Device 1
S1-1 S1-2 S1-3 S1-4 Jumpers for:
0 Close Close Close Close 981 Cyl 5 Heads
1 Open Close Open Close 987 Cyl 7 Heads
2 Close Open Close Open 612 Cyl 4 Heads
* 3 * Open Open Open Open 615 Cyl 4 Heads


S1-5 S1-6 Jumpers for:
Close Close RLL - 17 Sectors per Track (W9 ON )
* Open * Close * RLL - 26 Sectors per Track (W9 OFF)
Close Open RLL - 17 Sectors per Track (W9 OFF)
Open Open MFM - 17 Sectors per Track (W9 OFF)


S1-7 Jumper for:
Close IRQ 2 Select
* Open * IRQ 5 Select


S1-8 Jumper for:
Close AT Buss Mode
* Open * XT Buss Mode


* W3 * ON pins 1 & 2 Enable BIOS
W3 OFF pins 1 & 2 Disable BIOS

W4 ON pins 1 & 2 Device Address 0324H
* W4 * ON pins 2 & 3 Device Address 0320H

W6 ON pins 1 & 2 R.W.C. 9 - 16 Heads
* W6 * ON pins 2 & 3 R.W.C. 0 - 8 Heads

W8 ON pins 1 & 2 Secondary Controller
* W8 * ON pins 2 & 3 Primary Controller

W9 ON pins 1 & 2 Enable Firmware
* W9 * OFF pins 1 & 2 Disable Firmware


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WD-27X RLL Primary Format Procedure (BIOS 62-000089-030)


RLL Format begins at C800:0005 and requires two parameters:


A:\> DEBUG

-RAX ; AH = Drive 00 or 01 (Default = 00)
AX 0000 ; AL = Interleave 02 to 07 (Default = 04)
:0004 ; AX = 0004 Default
-G=C800:5


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DOS v3.3 Format Procedure


A:\> FDISK (Primary; Entire Drive; Active)

< Automatic Reboot >

A:\> FORMAT C:/S/V

A:\> CHKDSK C:*.*/F

32 Mb Drive shows 4 Heads, 614 Cylinders, 2Kb Clusters


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CORETEST v2.7 Benchmarks


Drive: Seagate ST-238R Everex 32 Mb Kit $325.00 JUL-87

Controller: WD1002-27X RLL BIOS: 62-000089-030 MPU: 1015E-08

Computer: Bullet 286-8 Mhz BUSS: XT 4.77 Mhz BIOS: Marchand



Interleave Transfer Rate Seek Track P.I. Configuration

3 27.0 Kb/sec 53.5 ms 15.6 ms 1.18 DOS 3.3 BUFFERS=18

4 26.1 Kb/sec 52.5 ms 14.5 ms 1.21 DOS 3.3 BUFFERS=18

5 25.3 Kb/sec 52.0 ms 15.6 ms 1.21 DOS 3.3 BUFFERS=18

* 6 * 115.3 Kb/sec 52.5 ms 13.0 ms 1.73 DOS 3.3 BUFFERS=18

6 3276.7 Kb/sec 57.5 ms 14.5 ms 20.46 DISCACHE /D:C/M:96



Review: The WD-27X RLL Controller and Seagate ST-238R Drive provide
32 Mb of mass storage at 55 ms for a penny a kilobyte. Data
Transfer Rates and optimal Interleave Factors no doubt vary
on different computers. Maximum rated Buss speed is 8 Mhz.
An optional WD SuperBios provides dynamic Drive Table setup
and enhanced performance.



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Western Digital Corporation


Phone Number: 1 800 847-6181 x4111 Literature Dept - Controller Info

Send $25.00 with request for WD SuperBios to:

Western Digital Corporation
Attention: Technical Support SuperBios
2445 McCabe Way, Irvine, CA 92714

Include specifications of your WD Controller:

For Example: WD1002-27X BIOS 62-000089-030 MPU 1015E-08

The SuperBios is part number: 62-000094-032


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Seagate Technology


Phone Number: 1 800 468-3472 x1 x2 Literature Dept - Drive Info

Seagate Technology
920 Disc Drive
Scotts Valley, CA 95066


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WD-27X.DOC Steve Shelton & Jim Bready Modulator PCBoard (408) 728-5598
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