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XT-IDE  Rev 1


This page is about the first revision of the XT-IDE card produced by the Vintage Computer Forums (VCF),  not the later second nor third revisions.

Production started in about 2009, and ended about 2012 when the second revision of the card was designed.
This revision of the card is typically referred to as 'XT-IDE Rev 1' or 'XT-IDE Revision 1' in order to distinguish it from the second revision of the card.


Photo / Identification

A photo of an XT-IDE Rev 1 card is here.
Printed on the card (left of the IDE connector) is "XT-IDE, REV 01".


Purpose / Description

It was long recognised that the MFM type hard drives associated (period correct) with the IBM XT (and clones), were becoming scarcer due to failure, and that replacement hard drive functionality was needed.

Although 8-bit IDE drives (and matching IDE cards) for the XT can still be found (on eBay, etc.), the quantity is very very low.

Members of the VCF decided to take advantage of the large nubers of 16-bit IDE drives (AT type IDE) that still exist.  They designed a card, named the XT-IDE, which interfaces 16-bit IDE drives to the 8-bit expansion bus of the IBM XT.  Click here to see a diagram.

Like other XT-class hard disk controllers, the XT-IDE has what is known as a 'BIOS expansion ROM'.  That ROM contains software, the 'XTIDE Universal BIOS', software that was developed for the XT-IDE card.  Rather than using a ROM of type EPROM, the XT-IDE designers chose instead to wire the card for an EEPROM.  That enables the contents to be updated/changed via a DOS program.


Hardware

The card consists of two hardware functionalities:
1.  IDE interface
2.  28C64 EEPROM and its support circuitry  (referred to as a 'boot ROM' in some XT-IDE documentation)

From a hardware perspective, the two are completely seperate; two circuits put onto one card.  For example, you could build an XT-IDE card omitting the 28C64 EEPROM and its supporting circuitry.  You would then put the XTIDE Universal BIOS into a ROM, placing that ROM into a (compatible) BIOS expansion ROM socket of a different card.


Software

As stated before, the XT-IDE card contains the 'XTIDE Universal BIOS' software in its EEPROM.

The XTIDE Universal BIOS is configurable (via the DOS program named XTIDECFG.COM).  For the first revision (Rev 1) of the XT-IDE card, there are two very important configuration options in XTIDE Universal BIOS: the bus type, and the base I/O address of the IDE interface.  Refer to the picture at here, which shows what the options look like in early versions of the XTIDE Universal BIOS.


Switch/jumper settings

A diagram is at here

It is critical to know that if you change the base I/O address of the IDE interface, then you will need to reconfigure the associated option of the XTIDE Universal BIOS within the EEPROM (so that the BIOS knows which I/O addresses to use).

The setting of jumper K1 is only relevant if you use the drive selection methodology of 'cable select' rather than the normally used methodology of master/slave.


Circuit diagram / Component list

Circuit diagram
Component list

In the component list, note the recommendation (or requirement?) for the Amtel brand of 28C64 EEPROM chip.  My further recommendation is that you use the 'B' verson of that chip, the AT28C64B instead of the AT28C64, because of problems I have seen using XTIDECFG.COM to program the AT28C64.


XTIDE Universal BIOS

Although later versions exist, version 1.1.4 and 1.1.5 are typical for XT-IDE Rev 1 cards.
Version 1.1.5 can be downloaded from here.

If you chose to use a later version (2.x.x) in the XT-IDE Rev 1, set the configuration option of 'device type' to 'XTIDE rev 1'.


Reprogramming the 28C64 EEPROM

A DOS program named XTIDECFG.COM was provided to do this.

Typical operation #1 - Programming XTIDE Universal BIOS into empty 28C64 EEPROM
         1.  Fit 28C64 EEPROM into card.
         2.  Ensure that jumpers JP1 and JP2 are both on.
         3.  Obtain BIN file of XTIDE Universal BIOS, e.g.  IDE_XT.BIN
         4.  Run XTIDECFG.COM - a menu is presented.
         5.  XTIDECFG.COM: Read in the IDE_XT.BIN file.
         6.  XTIDECFG.COM: Make any required configuration changes.
         7.  XTIDECFG.COM: Write the configuration to the EEPROM.  See note 1 below.

Typical operation #2 - Configuration change
         1.  Ensure that jumpers JP1 and JP2 are both on.
         2.  Run XTIDECFG.COM - a menu is presented.
         3.  XTIDECFG.COM: Choose to read the current contents of the EEPROM.
         4.  XTIDECFG.COM: Make any required configuration changes (e.g.  set new base address of the I/O range).
         5.  XTIDECFG.COM: Write the changed configuration back to the EEPROM.  See note 1 below.


NOTE 1:  There is a 'SDP command' option.  Photo here.  Disable that option if your EEPROM is the base version of the AT28C64.  Enable it if your EEPROM is the 'B' version, the AT28C64B.



Hardware defects

After the XT-IDE cards, of both Rev 1 and Rev 2, were produced, it was discovered that resistor R6 should be instead a link (Rev 2 photo).  This defect is only of concern if you use the drive selection methodology of 'cable select' rather than the normally used methodology of master/slave.


Incompatibilities

A few, mainly due to the fact that XT clones are never 100% copies.

Issues that were discovered will be discussed in the following VCF threads:
Main thread for XT-IDE
XTIDE Universal BIOS

I discuss one of the incompatibilities, one with the IBM 5170, below.


CF cards

Using a CF-to-IDE adapter, a CF card can be used in place of a 16-bit IDE drive.  An example adapter is pictured at here.

Such adapters require power, so ensure that they get power.

Do not expect all CF cards to work.

A common problem with newly purchased CF cards:

SYMPTOM	Although the normal FDISK and FORMAT/S commands had been performed against the CF card to make it bootable, the computer will not boot from the CF card.  The XTIDE Universal BIOS 'recognises' the CF card (it presents details of the card on-screen).  You discover that if you boot from floppy, the CF card is acessible (you can read/write/copy files on it).
CAUSE	Non-standard boot code in the MBR of the CF card.
FIX	Use the /MBR option of FDISK.EXE (from DOS version 5 or later) against the CF card.  So, after booting from a DOS 5 (or 6) boot floppy, enter: FDISK /MBR

Boot lockup due to damaged/misconfigured XTIDE Universal BIOS

Sometimes, a user may discover that their once booting computer (containing an XT-IDE card) now locks up during boot, and that the computer boots if the XT-IDE card is removed.

One known cause (of a few) is that, for whatever reason, the XTIDE Universal BIOS software within the EEPROM chip has become damaged/corrupt/improper. If that is the case, then the XTIDE Universal BIOS needs to be reloaded (or possibly just reconfigured).

But a catch-22 situation exists, because to load/reconfigure the XTIDE Universal BIOS using XTIDECFG.COM, the XT-IDE card needs to be present and the computer needs to boot.
One answer is to:
1. Remove jumper JP1 from the XT-IDE card. That action disables the EEPROM.
2. Put the XT-IDE card in the computer.
3. Power on the computer, booting from a floppy that contains XTIDECFG.COM
4. When the DOS prompt appears, put jumper JP1 back on.
5. Run XTIDECFG.COM



MODIFICATION:  IDE pin 20

Normally, for use with the XT-IDE rev 1 card, CF-to-IDE adapters and DOMs have to be externally powered, such as shown in the photo at here.

But some (repeat: some) can be optionally powered via pin 20 of the IDE interface connector.  On the XT-IDE Rev 1 card, pin 20 of the connector (P1) is not connected to anything. So, what some owners of XT-IDE Rev 1 cards did, was to solder on a wire that connected pin 20 of the IDE connector to +5 volts.  A photo of that modification is here.

An example of a CF-to-IDE adapter that can be powered via pin 20 is pictured at here.  One that cannot is pictured at here.


[ By the way. This modification was incorporated into revision 2 of the XT-IDE card (enabled/disabled via jumper P9). ]



MODIFICATION:  The 'Chuck mod'

Be aware that some XT-IDE Rev 1 cards were modified by their owner to incorporate what became known as the 'Chuck mod', and later, 'hi-speed'. The modification made the card perform faster. The modification involved changing the card's wiring, and using a specially hacked 1.x.x version of the XTIDE Universal BIOS.

This means is that, in effect, there are two versions of the XT-IDE Rev 1 cards in existance.

It is important to realise that this modification has both hardware and software components.


[ By the way. This modification was incorporated into revision 2 of the XT-IDE card (named 'hi-speed' mode) and into 2.x.x versions of the XTIDE Universal BIOS. ]



Coexistence with MFM hard drive controller card

The XT-IDE Rev 1 card can coexist with an XT-class MFM hard drive controller card.

A photo of such a hardware configuration is at here.  As shown here, when I power up the computer, the XTIDE Universal BIOS gives me the choice of hard drive booting from either the ST-225 drive (the "Foreign Hard Disk") or the CF card (the "SanDisk SDCFB-32").  I then use the up/down arrow keys on the keypad to select what I want to boot from, then press the ENTER key.

Make sure that the MFM drive is successfully booting before you add the XT-IDE card.



KNOWN PROBLEM:  IBM 5170 (IBM AT)

It is not normal to have an XT-IDE Rev 1 card in a 16-bit computer such as the IBM 5170.  Normally, for performance, a 16-bit IDE controller would be used (see bottom row of here).  But, if you are planning to add an XT-IDE Rev 1 card to an IBM 5170, be aware of an incompatibility between the XTIDE Universal BIOS and the 5170 motherboard's IBM BIOS ROMs:

* The result is corrupted reads of files (as evidenced by CRC comparisons).
* The degree/frequency of corruption is related the revision of the motherboard BIOS. There were three revisions. The more modern the revision, the less corruption.
* The symptom disappears entirely if the IBM BIOS is swapped out for a non-IBM one.