Heathkit H89 Emulator

for the iPad

Copyright 2011 by Les Bird


Update 10/15/2012:

Apple would not approve my emulator for the App Store because it allows you to run programs from the included library of disk images.

Update 01/17/2013:

Source code for the iPad Z89 emulator: iPadZ89Emu.zip (8 mb)

The Heathkit H89 Emulator for the iPad includes the HDOS 3.0 operating system and most of the original HUG library. This app emulates the Heathkit H89 8-bit computer from the early 80s. For more information on the Heathkit H89 computer system visit the SEBHC website.

To familiarize yourself with the HDOS 3 operating system, download the PDF manual here:
HDOS 3 Reference Manual

This reference manual is also included with the iPad app.


When you first launch the app you will see the Heathkit prompt (H:) at the top of the screen. The system has been booted to the ROM and is awaiting further commands. From here you want to select one of the included disk images and boot to the operating system.


Tap anywhere in the upper part of the screen to view the included disk images:

Heathkit H89 emulator for the iPad

Scroll the list by swiping up or down.

Tap on the floppy drive button labeled SY0: then tap on a disk image to insert into the emulated drive.


Important note: When you boot a distribution image for the first time it will appear that nothing is happening. You will see the H: prompt with a blinking cursor. The HDOS operating system is in the autobaud detect mode. Just tap the SPACEBAR on the keyboard a few times to continue the boot process.

To start off let's scroll down the list and select the HDOS_3-02_1_System.h8d disk image by tapping on it. Tap on the DONE button to close the disk image library and then tap the BOOT button to boot the emulator into the HDOS 3 operating system. You'll be asked to enter the current date.

Important node:
The HDOS operating system is not Y2K compliant so you cannot enter a year that is higher than 1999.

HDOS 3 boot screen

After you type in a date (or just tap RETURN to use the default) you will see the HDOS 3 prompt which looks like this:


HDOS is now waiting for commands. The first thing to do is configure HDOS for the type of terminal we are emulating, which is a Heathkit H19. Do this by typing in the following command:


Then press RETURN. Now restart HDOS by typing in the following:


After you see the logoff screen tap the RESET button then tap the BOOT button. You should now see a boot screen that looks like this:

Heathkit H89 emulator for the iPad

From the HDOS 3 prompt (S:) you can enter in any HDOS 3 command (see the reference manual) or execute one of the programs on the disk. All HDOS programs have an extension of .ABS and can be run directly from the prompt. Just type the program name and press the RETURN key.

I've included some shortcut buttons for some of the more common HDOS commands. These are labeled MOUNT, DIR, SET, SY0:, SY1: and SY2:. When you are at the S: prompt you can tap one of these shortcut buttons and the command will be typed in for you. As an example, to get a directory listing for the disk image in drive SY1: you can tap the DIR button followed by the SY1: button and then press the RETURN key.

There's a slide switch at the bottom of the screen labeled 2MHz. By default this switch is in the OFF position. This means the emulation is running as fast as the iPad can run it, which is pretty fast. Most of the time you probably want to leave this switch in the OFF position but if you are playing any of the games you'll want to switch it ON. Sliding this switch to the ON position will do two things. First, it will slow the emulator down to run at approximately 2MHz which is close to the speed of the real computer. Second it will turn off all filtering for the fonts so that graphic characters will look correct.


To view the disk image library just tap anywhere in the upper part of the screen. The disk image library is split into 2 categories called My Images and Distribution. The distribution section are disk images in their factory supplied condition. These images are exact copies of the disks that you would get from the factory, never booted and never written to. Once a disk image is written to or used in anyway, it is copied and added to the My Images section. You can delete any disk image from the My Images section by swiping it and tapping on the DELETE button. You can never delete or write to a disk image that is in the Distribution section. These are permanent unalterable backups.

There are 3 emulated floppy drives labeled SY0:, SY1: and SY2:. In most cases you want to insert a bootable operating system disk image into the SY0: drive. You can then insert another disk in SY1: or SY2: and access it from the operating system. Do this by first mounting the disk from the HDOS S: prompt like this:


But before you can do this you have to select a disk image and insert it into the drive. Tap in the upper part of the screen to pull up the disk image library then tap one of the drive letters, SY1: or SY2:, then tap on a disk image to insert into that drive. Now you can mount the disk using the above command and access it's contents from the HDOS operating system.

For a thorough description of the HDOS 3 operating system, read the included reference manual.

January 17, 2013