2018-10-13 14:18:13 -07:00

15 KiB

ROM 4X by MG

ROM 4X is a collection of enhancements to the Apple //c version 4. See the top level for more general information on ROM 4X and ROM 5X.

It adds the following features to the Apple //c:

- Enter the monitor unconditionally.
- Reboot the machine (enter standard boot sequence).
- Zero the RAM card, in case it is corrupted.
- Execute the machine and RAM card diagnostics.
- Tell the machine to boot the SmartPort, the internal floppy drive, or an external floppy drive.
- The system drops to BASIC if no bootable device is found (this is the default behavior in the IIc Plus).
- Configure default boot device by saving a file on the RAM Disk.
- As of the 10/01/2018 release, provides XModem-CRC features (see [](

RAM expansion cards known to work with ROM 4X include the Apple Memory Expansion Card (but no battery!), and the A2Heaven RAM Express II for the original //c, and the RAM Express II+ for the memory-expandable //c and IIc Plus.

User Guide


Due to copyright law, I do NOT provide full ready-to-burn binaries at this time. Some assembly (but not necessarily an assembler) is required!

You may either build it yourself which guarantees that you have the latest version and feature branch that you want, or you can check the web site for ROM 4X/5X for binary releases.

Binary Releases

The binary releases consist of a zip file with the assembled and linked patches, a checksum file, and a Bash script. You must have a unix-like system (MacOS, Linux, etc.) or, on Windows, Cygwin or the Windows Subsystem for Linux configured.

The shell script will perform the following:

  • Download the original Apple ROM image from a well-known location.
  • Apply the patches.
  • Validate the checksums of both the original ROM image and the patched ROM image.


Real System

Burn the ROM image (generally named iic_rom4x.bin) onto a 27C256 chip, or burn twice (into the lower and upper halves) of a 27C512 chip. If you can obtain an SST27SF512 flash EEPROM, that is a great option.

Once you have a ROM chip, generally the instructions here are relevant. You won't need to cut any traces or solder a jumper unless you are installing this ROM in an original //c.


The following emulators are known to run ROM 4X:

  • MAME (replace the image for the apple2c4 machine).
  • Leon Bottou's "universal" versions of GSPlus and KEGS.
  • Catakig (older emulator for MacOS, will stop working on Mojave).

Copy the ROM image into the appropriate location for your emulator.



Power on your machine. Everything should look and work almost like it did before. If there is a bootable device somewhere, the machine will boot it. If there is not (and this is one of the noticable changes), you will get dropped to BASIC without the need to press ctrl+reset. If things don't go well, revisit your installation.

If you don't have an initialized RAM disk, format the card RAM disk with something like Copy II Plus. Put ProDOS and BASIC.SYSTEM on it. Power off the machine, and power it on after a few minutes. You should boot off of the RAM disk. You might notice an "R" flash on the screen for an instant before ProDOS loads.

Now, press Control+Closed-Apple+Reset, holding down Closed-Apple after releasing reset. You should see the following menu appear:

0 Monitor
1 Reboot
2 Zero RAM Card and Reboot
3 Diagnostics
4 RAM Card Diagnostics
5 Boot SmartPort
6 Boot Int. 5.25
7 Boot Ext. 5.25

Picking any of the menu options besides 0 results in the menu being cleared, but the bottom line 'ROM 4X mm/dd/yy' immediately reappears to confirm that the new code is taking action.

What each option does is detailed below. Note that the various device boot options will try that device and any remaining devices in the boot order, which for the Apple //c is RAM card, 5.25 drive, and finally SmartPort.

0 Monitor

This drops you unconditionally into the monitor.

1 Reboot

This carries out the normal boot sequence, which is to try the RAM disk first, then the internal 5.25 floppy drive, then the first connected smartport device. Some of the other options let you skip over one or more of this ordering.

2 Zero RAM Card and Reboot

This zeros out the RAM card memory and the screen holes. This is a nuclear option if the RAM disk is corrupt and the system fails to boot. After selecting 2 the word "SURE?" appears on the screen. At this point you must type Y or y to continue with the zeroing, or any other key to cancel.

If there is no card RAM, you are immediately rebooted. Otherwise an 'A' will appear in the upper left corner of the screen and will follow the alphabet as each 64K of the card is cleared. After it completes the letter will disappear and the machine will try booting.

3 Diagnostics

This jumps to the //c internal diagnostics that are also run when you press control+both-apples+reset.

4 RAM Card Diagnostics

This runs the RAM card diagnostics. When the diagnostics are finished either by user cancel or error, you are dropped into the monitor.

Since the test may damage data on the card, you are asked to confirm as per option 2 above.

5 Boot SmartPort

This attempts to boot the first smartport device, such as a UniDisk 3.5.

6 Boot Internal 5.25

This skips the RAM disk and starts booting with the internal 5.25 drive.

7 Boot External 5.25

This is like option 6, but using an external 5.25 drive. The only OS I am aware of that supports booting this way is ProDOS.

This destructively copies a short routine to $800, which under most circumstances is also immediately overwritten by the boot sector, so should not be a problem..



Configuration File

If the RAM card is ProDOS-formatted, you can save a binary file in the volume directory called BOOTX. ROM 4X will find this file and use the Aux Type field (the load address) to set a default of the menu options above when no option has been selected using the menu. For example, BSAVE /RAM4/BOOTX,A6,L0 will cause ROM 4X to skip booting the RAM card and go straight to booting the internal floppy drive (menu item 6). The contents of BOOTX are irrelevant, only the Aux Type is used. You cannot set it to jump into the monitor because that action happens before the boot code takes over.

You will know the configuration file is being used because the ROM 4X line will appear on the bottom of the screen and a flashing 'C' will appear in the lower-left corner.

WARNING: You can set the BOOTX file to clear the RAM card or run the RAM card diagnostics. This will happen exactly once and your RAM disk will be gone. Caveat emptor.

Build/Develop Guide


To build the new firmware, you must start with a copy of the repository, and obtain a copy of the Apple //c version 4 ROM. The patches to the firmware work with the ROM dump that has sha256sum:


It may work with other ROM dumps, it will not work with any other ROM versions, including ROM 3 and earlier. You must build ROM 4X using a ROM 4 dump.

The Rakefile will download the file from a well-known location if it is not already present. It also verifies the checksum.

Now you will need a 65C02 cross assembler. The current codebase is developed using ca65 from the cc65 project. Only the assembler and linker are required. Older versions may complain about argument order, generally versions identifying as "2.16" built from the ca65 git master branch work fine.

Finally you will need Ruby and Rake.

Once you have it all together change to the directory with the source files and original ROM image and type rake.

If all goes well, you will have a shiny new iic_rom4x.bin.

If you intend to build an image for a 512-kbit chip such as the SST27SF512, do rake sf512.


First Thing's First

First and foremost, it is most helpful to have an emulator. The only one that I have found that can be used for (almost) thorough testing is Catakig for MacOS. It can emulate the //c and the Expansion Card (though not battery-backed).

If you plan to test on a real machine, be aware that the ROM socket is not rated for a large number of insertions and you will break something after a while. You may consider putting a machine-pin DIP socket or a ZIF socket into the CPU socket position. This can be done by desoldering the original socket if you have the skills, or by plugging the new socket into the existing CPU socket. If you do do the latter you should consider the new socket permanent as the socket pins are thicker than a ROM chip's and removing it may leave the socket in such a state as to not be able to make good contact with a subsequent chip.

As for me, I just use the emulator and then I am very careful with changing the ROM when I want to test on the real hardware. For heavy development/testing I insert a low-profile solder-tail ZIF socket into the existing chip socket..

Apple //c Technical Reference and other Documentation

You need this.

The Apple //c Technical Reference Manual that is available on the internet has the firmware listing for ROM 3. ROM 4 fixes a few bugs that were in ROM 3, including with the memory card driver. The changes are minor and affect some of the offsets of routines in the RAM card support, but it is easy to figure them out.

This tech note is also helpful as it documents the screen holes and some of the card behavior including under what conditions it reformats. Though the power2 byte is not used by the Apple //c code -- it is commented out in the firmware listings in the Technical Reference. ROM 4X uses it for the menu function.

This technical note is a little less helpful for this project.

Magic File Names

The main source files are named after a pattern, B#_####_something.s where the first # represents the bank number (0 = main, 1 = aux), and #### is the location in the bank to patch the code into. E.G. the B1_E000_rom4.bin's object code is loaded into bank 1 at E000. Generally the origin address of the code in the file matches the #### portion of the file name.

The Rakefile uses this information to patch the original ROM 4 and produce the ROM 4X version.


One file, iic.defs is included by all of the other source files. This has entry points, origins, and various RAM locations defined in it for use by the other source code.

Test Scenarios

Basic Functional Tests

  1. Boot ProDOS from power off. Run SlotScan 1.62 and confirm that the slots are identified as expected, see below.
  2. With no bootable ProDOS RAMdisk, boot the system from power off or ctrl-oa-reset. 1. With the drop-to-basic patch:
    • Expected: The system says "No bootable device" and drops to BASIC. 2. Without to drop-to-basic patch:
    • Expected: The system boots the same as an unmodified ROM 4.
  3. With a bootable ProDOS RAMdisk containing ProDOS, boot the system from power off or ctrl-oa-reset. - Expected: The system boots from RAM disk, an inverse or flashing R may appear on the left of line 24 of the display.
  4. Power on the system with the ca key pressed or use ctrl-ca-reset. - Expected: The menu is displayed.
  5. RAM disk recovery: 1. Battery-backed RAM present with bootable RAM disk: Power off the machine and leave it for 1 hr. Power on.
    • Expected: The system boots from RAM disk. 2. Non-battery-backed RAM present with bootable RAM disk: Erase main RAM from 0300 up (e.g. in monitor: 300:00 then 301<300.BFFEM) and press ctrl-reset.
    • Expected: The system boots from RAM disk.

Expected SlotScan output:

SlotScan  Version 1.62                  Copyright 1989-1994 by Robert S. Claney 
Apple Computer Type: //c, ROM Ver 4 (Newer Mem. Exp.)                           
Processor type: 65c02                                                           
Total RAM: 128K                                                                 
-----Scanning for peripherals-----                                              
Port 1: Serial Port (#1)                                                        
Port 2: Serial Port (#1)                                                        
Port 3: 80-Column Port (#8)                                                     
Port 4: RamCard SmartPort: 1 device found                                       
        Manufacturer #0 (Unknown)                                               
        Device 1: "RAMCARD",  Size: 2048 Blocks (1024K, 1 Meg)                  
             Type: Mem. expansion    Version: 0.102                             
             Addl. info:  (None)                                                
Port 5: SmartPort: 0 devices found                                              
Port 6: Disk ][ Port                                                            
        Device Size: 280 Blocks (140K)                                          
Port 7: Mouse Port (#0)                                                         
Done.  Press any key to continue, or Control-P to get a printout             

Menu Item Functional Tests

All cases: When any menu option is selected, the "ROM 4X MM/DD/YY" message is displayed on the bottom of the screen.

  1. Monitor - Expected: We are dropped into the monitor immediately.
  2. Reboot - Expected: System boots as normal.
  3. Zero RAM Card and Reboot - Expected: Reboot if no card RAM present. Otherwise, counter appears in upper left corner and card RAM is cleared.
  4. Diagnostics - Expected: System enters built-in diagnostics as if ctrl-oa-ca-reset was pressed.
  5. RAM Card Diagnostics - Expected: System enters RAM card diagnostics if card RAM present, then/or (no mem) drops to monitor when exited by failure or user escape key.
  6. Boot SmartPort - Expected: The system boots from a SmartPort device, skipping the RAM card and 5.25 floppy drives.
  7. Boot Internal 5.25 - Expected: The system boots from the internal 5.25 drive, skipping the RAM card. The system may proceed to the SmartPort if no disk is found.
  8. Boot External 5.25 - Expected: The system boots from the external 5.25 drive, skipping the RAM card. The system may proceed to the SmartPort if no disk is found.

Ideas for Future

  • Replace Apple Slinky code with RamFactor code. (Difficulty: Hard)